#include <cstdio>
#include <algorithm>
#include <utility>

using namespace std;

const int N = 16390, inf = (1ll << 31) - 1;

struct CODE{
    int c1, c2, ind;
};

char s [N];
CODE cod [N];
int n, lim, poz [15][N];
pair <int, int> c [N];

class MyComp {
public :
    bool operator () (const CODE &A, const CODE &B) {
        return A.c1 < B.c1 || (A.c1 == B.c1 && A.c2 < B.c2);
    }
};

class MyComp2 {
public :
    bool operator () (const pair <int, int> &A, const pair <int, int> &B) {
        return A.first < B.first;
    }
};


void suffixarray () {
    int i, j, l;

    for (i = 0; i < n; i ++)
        poz [0][i] = s [i] - '0';
    for (j = 1; (1 << j) < n; ++ j) {
        lim = j;
        l = (1 << (j - 1));
        for (i = 0; i < n; i ++) {
            cod [i].c1 = poz [j - 1][i];
            if (i + l + l - 1 < n)
                cod [i].c2 = poz [j - 1][i + l];
            else cod [i].c2 = -1;
            cod [i].ind = i;
        }
        sort (cod, cod + n, MyComp ());
        for (i = 0; i < n; i ++)
            if (i > 0 && cod [i].c1 == cod [i - 1].c1 && cod [i].c2 == cod [i - 1].c2)
                poz [j][cod [i].ind] = poz [j][cod [i - 1].ind];
            else
                poz [j][cod [i].ind] = i;
    }
}

int lcp (int x, int y) {
    int j, step, l = 0;
    if (x == y)
        return n - x;
    for (j = lim; j >= 0 && x < n && y < n; j --)
        if (poz [j][x] == poz [j][y]) {
            x = x + (1 << j);
            y = y + (1 << j);
            l = l + (1 << j);
        }
    return l;
}

int main () {
    int k, i, ans = 0;

    freopen ("substr.in", "r", stdin);
    freopen ("substr.out", "w", stdout);

    scanf ("%d%d", &n, &k);
    scanf ("%s", s);
    suffixarray ();
    for (i = 0; i < n; i ++) {
        c [i].first = poz [lim][i];
        c [i].second = i;
    }
    sort (c, c + n, MyComp2 ());
    for (i = 0; i < n; i ++) {
        if (i + k - 1 < n)
            ans = max (ans, lcp (c [i].second, c [i + k - 1].second));
    }
    printf ("%d\n", ans);
    return 0;
}