/+ dub.sdl:
    name "A"
    dependency "dcomp" version=">=0.6.0"
+/

import std.stdio, std.algorithm, std.range, std.conv;
import std.typecons;
// import dcomp.foundation, dcomp.scanner;

// import dcomp.algorithm;
// import dcomp.string;

int main() {
    auto sc = new Scanner(stdin);
    int k;
    string s;
    sc.read(k, s); k++;
    int n = s.length.to!int;

    if (n % k == 0) {
        int c = n/k;
        string ans = ":";
        foreach (i; 0..k) {
            ans = max(ans, s[c*i..c*(i+1)]);
        }
        writeln(ans);
        return 0;
    }
    int c = (n+k-1)/k;
    auto sai = suffixArray(s);
    bool calc(int x) {
        int p = sai.sa[x];
        string base = s[p..min($, p+c)];
        int nw = 0;
        foreach (i; 0..k) {
            if (n <= nw) break;
            string t = s[nw..min($, nw+c)];
            if (t <= base) {
                nw += c;
            } else {
                nw += c-1;
            }
        }
        return n <= nw;
    }
    auto u = sai.sa[binSearch!(x => calc(x))(0, n+1)];
    writeln(s[u..u+c]);
    return 0;
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/scanner.d */
// module dcomp.scanner;

class Scanner {
    import std.stdio : File;
    import std.conv : to;
    import std.range : front, popFront, array, ElementType;
    import std.array : split;
    import std.traits : isSomeChar, isStaticArray, isArray; 
    import std.algorithm : map;
    File f;
    this(File f) {
        this.f = f;
    }
    char[512] lineBuf;
    char[] line;
    private bool succ() {
        import std.range.primitives : empty, front, popFront;
        import std.ascii : isWhite;
        while (true) {
            while (!line.empty && line.front.isWhite) {
                line.popFront;
            }
            if (!line.empty) break;
            if (f.eof) return false;
            line = lineBuf[];
            f.readln(line);
        }
        return true;
    }

    private bool readSingle(T)(ref T x) {
        import std.algorithm : findSplitBefore;
        import std.string : strip;
        import std.conv : parse;
        if (!succ()) return false;
        static if (isArray!T) {
            alias E = ElementType!T;
            static if (isSomeChar!E) {
                //string or char[10] etc
                //todo optimize
                auto r = line.findSplitBefore(" ");
                x = r[0].strip.dup;
                line = r[1];
            } else {
                auto buf = line.split.map!(to!E).array;
                static if (isStaticArray!T) {
                    //static
                    assert(buf.length == T.length);
                }
                x = buf;
                line.length = 0;
            }
        } else {
            x = line.parse!T;
        }
        return true;
    }
    int read(T, Args...)(ref T x, auto ref Args args) {
        if (!readSingle(x)) return 0;
        static if (args.length == 0) {
            return 1;
        } else {
            return 1 + read(args);
        }
    }
}



unittest {
    import std.path : buildPath;
    import std.file : tempDir;
    import std.algorithm : equal;
    import std.stdio : File;
    string fileName = buildPath(tempDir, "kyuridenanmaida.txt");
    auto fout = File(fileName, "w");
    fout.writeln("1 2 3");
    fout.writeln("ab cde");
    fout.writeln("1.0 1.0 2.0");
    fout.close;
    Scanner sc = new Scanner(File(fileName, "r"));
    int a;
    int[2] b;
    char[2] c;
    string d;
    double e;
    double[] f;
    sc.read(a, b, c, d, e, f);
    assert(a == 1);
    assert(equal(b[], [2, 3]));
    assert(equal(c[], "ab"));
    assert(equal(d, "cde"));
    assert(e == 1.0);
    assert(equal(f, [1.0, 2.0]));
}

unittest {
    import std.path : buildPath;
    import std.file : tempDir;
    import std.algorithm : equal;
    import std.stdio : File, writeln;
    import std.datetime;
    string fileName = buildPath(tempDir, "kyuridenanmaida.txt");
    auto fout = File(fileName, "w");
    foreach (i; 0..1_000_000) {
        fout.writeln(3*i, " ", 3*i+1, " ", 3*i+2);
    }
    fout.close;
    writeln("Scanner Speed Test(3*1,000,000 int)");
    StopWatch sw;
    sw.start;
    Scanner sc = new Scanner(File(fileName, "r"));
    foreach (i; 0..500_000) {
        int a, b, c;
        sc.read(a, b, c);
        assert(a == 3*i);
        assert(b == 3*i+1);
        assert(c == 3*i+2);
    }
    foreach (i; 500_000..700_000) {
        int[3] d;
        sc.read(d);
        int a = d[0], b = d[1], c = d[2];
        assert(a == 3*i);
        assert(b == 3*i+1);
        assert(c == 3*i+2);
    }
    foreach (i; 700_000..1_000_000) {
        int[] d;
        sc.read(d);
        assert(d.length == 3);
        int a = d[0], b = d[1], c = d[2];
        assert(a == 3*i);
        assert(b == 3*i+1);
        assert(c == 3*i+2);
    }
    writeln(sw.peek.msecs, "ms");
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/foundation.d */
// module dcomp.foundation;
//fold(for old compiler)
static if (__VERSION__ <= 2070) {
    template fold(fun...) if (fun.length >= 1) {
        auto fold(R, S...)(R r, S seed) {
            import std.algorithm : reduce;
            static if (S.length < 2) {
                return reduce!fun(seed, r);
            } else {
                import std.typecons : tuple;
                return reduce!fun(tuple(seed), r);
            }
        }
    }
    unittest {
        import std.stdio;
        auto l = [1, 2, 3, 4, 5];
        assert(l.fold!"a+b"(10) == 25);
    }
}
version (X86) static if (__VERSION__ < 2071) {
    int bsf(ulong v) {
        foreach (i; 0..64) {
            if (v & (1UL << i)) return i;
        }
        return -1;
    }
    int bsr(ulong v) {
        foreach_reverse (i; 0..64) {
            if (v & (1UL << i)) return i;
        }
        return -1;   
    }
    int popcnt(ulong v) {
        int c = 0;
        foreach (i; 0..64) {
            if (v & (1UL << i)) c++;
        }
        return c;
    }
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/ascii.d */
// module dcomp.ascii;

struct ASCIIString {
    string s;
    alias s this;
    this(string s) {
        this.s = s;
    }
    ref immutable(char) front() const {
        return s[0];
    }
    void popFront() {
        s = s[1..$];
    }
    ref immutable(char) back() const {
        return s[$-1];
    }
    void popBack() {
        s = s[0..$-1];
    }
}

ASCIIString ascii(string s) {
    return ASCIIString(s);
}

unittest {
    import std.algorithm;
    import std.range.primitives;
    auto s = "タネなし手品";
    auto asc = s.ascii;
    assert(s.front == 'タ');
    assert(asc.front == "タ"[0]);
    assert(s.back == '品');
    assert(asc.back == "品"[$-1]);
    assert(asc.map!(c => 1).sum == s.length);
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/algorithm.d */
// module dcomp.algorithm;

import std.range.primitives;
import std.traits : isFloatingPoint, isIntegral;

//[0,0,0,...,1,1,1]で、初めて1となる場所を探す。pred(l) == 0, pred(r) == 1と仮定
T binSearch(alias pred, T)(T l, T r) if (isIntegral!T) {
    while (r-l > 1) {
        T md = (l+r)/2;
        if (!pred(md)) l = md;
        else r = md;
    }
    return r;
}

T binSearch(alias pred, T)(T l, T r, int cnt = 60) if (isFloatingPoint!T) {
    foreach (i; 0..cnt) {
        T md = (l+r)/2;
        if (!pred(md)) l = md;
        else r = md;
    }
    return r;
}

Rotator!Range rotator(Range)(Range r) {
    return Rotator!Range(r);
}

struct Rotator(Range)
if (isForwardRange!Range && hasLength!Range) {
    size_t cnt;
    Range start, now;
    this(Range r) {
        cnt = 0;
        start = r.save;
        now = r.save;
    }
    this(this) {
        start = start.save;
        now = now.save;
    }
    @property bool empty() {
        return now.empty;
    }
    @property auto front() {
        assert(!now.empty);
        import std.range : take, chain;
        return chain(now, start.take(cnt));
    }
    @property Rotator!Range save() {
        return this;
    }
    void popFront() {
        cnt++;
        now.popFront;
    }
}


E minimum(alias pred = "a < b", Range, E = ElementType!Range)(Range range, E seed)
if (isInputRange!Range && !isInfinite!Range) {
    import std.algorithm, std.functional;
    return reduce!((a, b) => binaryFun!pred(a, b) ? a : b)(seed, range);
}

ElementType!Range minimum(alias pred = "a < b", Range)(Range range) {
    assert(!range.empty, "range must not empty");
    auto e = range.front; range.popFront;
    return minimum!pred(range, e);
}

E maximum(alias pred = "a < b", Range, E = ElementType!Range)(Range range, E seed)
if (isInputRange!Range && !isInfinite!Range) {
    import std.algorithm, std.functional;
    return reduce!((a, b) => binaryFun!pred(a, b) ? b : a)(seed, range);
}

ElementType!Range maximum(alias pred = "a < b", Range)(Range range) {
    assert(!range.empty, "range must not empty");
    auto e = range.front; range.popFront;
    return maximum!pred(range, e);
}

unittest {
    assert(minimum([2, 1, 3]) == 1);
    assert(minimum!"a > b"([2, 1, 3]) == 3);
    assert(minimum([2, 1, 3], -1) == -1);
    assert(minimum!"a > b"([2, 1, 3], 100) == 100);

    assert(maximum([2, 1, 3]) == 3);
    assert(maximum!"a > b"([2, 1, 3]) == 1);
    assert(maximum([2, 1, 3], 100) == 100);
    assert(maximum!"a > b"([2, 1, 3], -1) == -1);
}

bool[ElementType!Range] toMap(Range)(Range r) {
    import std.algorithm : each;
    bool[ElementType!Range] res;
    r.each!(a => res[a] = true);
    return res;
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/string.d */
// module dcomp.string;

struct SA(T) {
    T[] s;
    int[] sa, rsa, lcp;
    this(in T[] s) {
        size_t n = s.length;
        this.s = s.dup;
        sa = new int[](n+1);
        rsa = new int[](n+1);
        lcp = new int[](n);
    }
}

int[] sais(T)(in T[] _s, int B = 200) {
    import std.conv, std.algorithm, std.range;
    int n = _s.length.to!int;
    int[] sa = new int[](n+1);
    if (n == 0) return sa;

    auto s = _s.map!"a+1".array ~ T(0); B++; // add 0 to last
    // ls
    bool[] ls = new bool[](n+1);
    ls[n] = true;
    foreach_reverse (i; 0..n) {
        ls[i] = (s[i] == s[i+1]) ? ls[i+1] : (s[i] < s[i+1]);
    }
    // sum(l[0], s[0], l[1], s[1], ...)
    int[] sumL = new int[](B+1), sumS = new int[](B+1);        
    s.each!((i, c) => !ls[i] ? sumS[c]++ : sumL[c+1]++);
    foreach (i; 0..B) {
        sumL[i+1] += sumS[i];
        sumS[i+1] += sumL[i+1];
    }

    void induce(in int[] lms) {
        sa[] = -1;
        auto buf0 = sumS.dup;
        foreach (d; lms) {
            sa[buf0[s[d]]++] = d;
        }
        auto buf1 = sumL.dup;
        foreach (v; sa) {
            if (v >= 1 && !ls[v-1]) {
                sa[buf1[s[v-1]]++] = v-1;
            }
        }
        auto buf2 = sumL.dup;
        foreach_reverse (v; sa) {
            if (v >= 1 && ls[v-1]) {
                sa[--buf2[s[v-1]+1]] = v-1;
            }
        }
    }
    
    int[] lms = iota(1, n+1).filter!(i => !ls[i-1] && ls[i]).array;
    int[] lmsMap = new int[](n+1);
    lmsMap[] = -1; lms.each!((i, v) => lmsMap[v] = i.to!int);

    induce(lms);
    
    if (lms.length >= 2) {
        int m = lms.length.to!int - 1;
        // sort lms
        auto lms2 = sa.filter!(v => lmsMap[v] != -1).array;
        int recN = 1;
        int[] recS = new int[](m);
        recS[lmsMap[lms2[1]]] = 1;
        foreach (i; 2..m+1) {
            int l = lms2[i-1], r = lms2[i];
            int nl = lms[lmsMap[l]+1], nr = lms[lmsMap[r]+1];
            if (cmp(s[l..nl+1], s[r..nr+1])) recN++;
            recS[lmsMap[lms2[i]]] = recN;
        }
        //re induce
        induce(lms.indexed(sais!int(recS, recN)).array);
    }

    return sa;
}

SA!T suffixArray(T)(in T[] _s, int B = 200) {
    import std.conv, std.algorithm;
    int n = _s.length.to!int;
    auto saInfo = SA!T(_s);
    if (n == 0) return saInfo;
    
    with (saInfo) {
        sa = sais(_s, B);
        //rsa
        sa.each!((i, v) => rsa[v] = i.to!int);
        //lcp
        int h = 0;
        foreach (i; 0..n) {
            int j = sa[rsa[i]-1];
            if (h > 0) h--;
            for (; j+h < n && i+h < n; h++) {
                if (s[j+h] != s[i+h]) break;
            }
            lcp[rsa[i]-1] = h;
        }
    }
    return saInfo;
}

unittest {
//     import dcomp.ascii;
    import std.algorithm, std.conv, std.stdio;
    import std.random;
    import std.typecons;
    import std.datetime;

    SA!T naive(T)(in T[] s) {
        int n = s.length.to!int;
        auto res = SA!T(s);
        res.s = s.dup;
        alias P = Tuple!(string, int);
        P[] buf = new P[](n+1);
        foreach (i; 0..n+1) {
            buf[i] = P(s[i..$].idup, i);
        }
        sort(buf);
        foreach (i, v; buf) {
            res.sa[i] = v[1];
        }
        foreach (i; 0..n+1) {
            res.rsa[res.sa[i]] = i;
        }
        foreach (i; 0..n) {
            res.lcp[i] = commonPrefix(buf[i][0], buf[i+1][0]).length.to!int;
        }
        return res;
    }

    writeln("SAIS Random100000");
    void f() {
        int n = uniform(1, 100);
        ASCIIString s;
        foreach (j; 0..n) {
            s ~= uniform('a', 'z');
        }
        auto l = naive(s);
        auto r = suffixArray(s);
        assert(equal(l.s, r.s));
        assert(equal(l.sa, r.sa));
        assert(equal(l.rsa, r.rsa));
        assert(equal(l.lcp, r.lcp));
    }
    auto ti = benchmark!f(10000);
    writeln(ti[0].msecs, "ms");
}
