#include <cstdio>
#include <cstring>
#include <map>
#include <algorithm>
#include <tr1/unordered_map>
using namespace std;

#define N 17000
#define M1 1000000003
#define M2 2000003
char a[N];
int n, K;

int isOk(int len) {
    tr1::unordered_map<int, int> H1, H2;
    tr1::unordered_map<int, int>::iterator it, jt;
    int i;
    int nr1 = 0, nr2 = 0;
    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) {
            it = H1.find(h1);
            jt = H2.find(h2);
            if (it == H1.end()) {
                H1.insert(make_pair(h1, 1));
                nr1 = 1;
            }
            else {
                ++it->second;
                nr1 = it->second;
            }
            if (jt == H2.end()) {
                H2.insert(make_pair(h2, 1));
                nr2 = 1;
            }
            else {
                ++jt->second;
                nr2 = jt->second;
            }
            
            //H1[h1]++;
            //H2[h2]++;
            int nr = min(nr1, nr2);//min(H1[h1], H2[h2]);
            //printf ("(l: %d r:%d) (h1: %d h2: %d) (%d %d)\n", i - len + 1,
            //        i, h1, h2, H1[h1], H2[h2]);
            if (nr >= K)
                return true;
            h1 = ((h1 - (pw1 * a[i - len + 1])) % M1 + M1) % M1;
            h2 = ((h2 - (pw2 * a[i - len + 1])) % M2 + M2) % M2;
        }
    }
    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;// 1 + (n / K);
    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);
}