#include <cstdio>
#include <cstring>
#include <map>
#include <algorithm>
#include <vector> 
using namespace std;
 
#define N 17000
#define M1 666013
#define M2 2000003
char a[N];
int n, K;
 
int H1[M1], H2[M2];
vector<int> remove_H1, remove_H2;

// remove only the necessary hash values
void remove() {
    for (int i = 0; i < remove_H1.size(); ++i)
        H1[ remove_H1[i] ] = 0;
    for (int i = 0; i < remove_H2.size(); ++i)
        H2[ remove_H2[i] ] = 0;
}
int isOk(int len) {
    //map<int, int> H1, H2;
    int i;
    int h1 = 0, h2 = 0;
    int pw1 = 1, pw2 = 1;
    for (i = 1; i < len; ++i)
        pw1 = (pw1 * 257) % M1,
        pw2 = (pw2 * 259) % M2;
     
    for (i = 1; i <= n; ++i) {
        h1 = (h1 * 257 + a[i]) % M1;
        h2 = (h2 * 259 + a[i]) % M2;
        
        if (i >= len) {
            H1[h1]++;
            H2[h2]++;
            remove_H1.push_back(h1);
            remove_H2.push_back(h2);
            int nr = min(H1[h1], H2[h2]);
            if (nr >= K) {
                remove();
                return true;
            }
            h1 = ((h1 - (pw1 * a[i - len + 1]) % M1) % M1 + M1) % M1;
            h2 = ((h2 - (pw2 * a[i - len + 1]) % M2) % M2 + M2) % M2;
        }
    }
    remove();
    return false;
}
 
int main() {
    freopen ("substr.in", "r", stdin);
    freopen ("substr.out", "w", stdout);
    scanf ("%d %d\n", &n, &K);
    scanf ("%s", a + 1);
 
    int i, cnt;
    int nr = n;
    for (cnt = 1; cnt * 2 <= nr; cnt *= 2);
    for (i = 1; cnt; cnt >>= 1)
        if (i + cnt <= n && isOk(i + cnt))
            i += cnt;
     
    printf ("%d\n", i);
}