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

/// Number of k-combinations
T combination(T = long)(T n, T k)
{
    assert(0 <= k);
    assert(0 <= n);
    if (n < k)
        return 0;
    k = min(n - k, k);
    if (k == 0)
        return 1;
    if (k == 1)
        return n;
    return memoize!combination(n - 1, k - 1) + memoize!combination(n - 1, k);
}

void main()
{
    long N = lread();
    long[][] A;
    foreach (_; 0 .. N)
    {
        A ~= aryread().map!"a-1"().array();
    }
    auto ptr = new long[N];
    long ans;
    long cnt;
    auto used = new bool[](N);
    while (true)
    {
        bool b = false;
        used[] = false;
        foreach (i; 0 .. N)
            foreach (j; i + 1 .. N)
            {
                if (N - 1 <= ptr[i] || N - 1 <= ptr[j] || used[i] || used[j])
                {
                    continue;
                }
                if (A[i][ptr[i]] == j && A[j][ptr[j]] == i)
                {
                    ptr[i]++;
                    ptr[j]++;
                    used[i] = used[j] = true;
                    // writefln("%d %d", i, j);
                    b = true;
                    cnt++;
                }
            }
        if (!b)
        {
            writeln(-1);
            return;
        }
        ans++;
        if (cnt == N * (N - 1) / 2)
        {
            break;
        }
        // writeln();
    }
    writeln(ans);
}
