import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv, std.math,
    std.functional, std.numeric, std.range, std.stdio, std.string, std.random,
    std.typecons, std.container, std.format;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
alias PQueue = BinaryHeap!(Array!long, "a<b");
// dfmt on

void main()
{
    long N = lread();
    auto S = sread();
    bool[string] set;
    long ans;
    foreach (i; 0 .. N)
    {
        foreach (len; 1 .. N)
            if (i + len <= (N + 1) / 2 && (S[i .. i + len]!in set))
            {
                set[S[i .. i + len]] = true;
                inner: foreach (j; i + len .. N + 1 - len)
                    if (S[i .. i + len] == S[j .. j + len])
                    {
                        writeln(S[i .. i + len]);
                        ans = ans.max(len);
                        break inner;
                    }
            }
    }
    writeln(ans);
}
