#include <bits/stdc++.h>
#define P ((int)1e9+7)
using namespace std;
ifstream fin("substr.in");
ofstream fout("substr.out");
unordered_map<int, int> M;
char text[16400];
int n, k, p62[16385];

void Make62()
{
    p62[0] = 1;
    for (int i = 1; i <= 16384; i++)
        p62[i] = 1LL * p62[i - 1] * 62 % P;
}

int Cod(char c)
{
    if (c <= '9') return c - '0';
    if (c <= 'Z') return c - 'A' + 10;
    return c - 'a' + 36;
}

int Verifica(int L)
{
    M.clear();
    int i, x = 0, e;
    e = p62[L - 1];
    for (i = 0; i < L; i++)
        x = (1LL * x * 62 + Cod(text[i])) % P;
    M[x]++;
    for ( ; text[i] != 0; i++)
    {
        x = (1LL * (x - 1LL * Cod(text[i-L]) * e % P + P) * 62 % P + Cod(text[i])) % P;
        M[x]++;
        if (M[x] >= k) return 1;
    }
    return 0;
}

int CautBin()
{
    int st, dr, L, mid;
    st = 1; L = dr = n - k + 1;
    while (st <= dr)
    {
        mid = (st + dr) / 2;
        if (Verifica(mid) == 1)
        {
            L = mid;
            st = mid + 1;
        }
        else dr = mid - 1;
    }
    return L;
}

int main()
{
    fin >> n >> k;
    fin >> text;
    Make62();
    fout << CautBin();
    fout.close();
    return 0;
}