#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
 
const int MAXN = 65536;
const int MAXLG = 17;
 
char A[MAXN];
struct entry {
    int nr[2], p;
} L[MAXN];
int P[MAXLG][MAXN], N, i, stp, cnt, q;
 
bool cmp(const entry &a, const entry &b) {
    return a.nr[0] == b.nr[0] ? (a.nr[1] < b.nr[1]) : (a.nr[0] < b.nr[0]);
}

void print_p() {
    for(int k = 0; k < stp; ++k) {
        for(int i = 0; i < N; ++i) {
            printf("%d ", P[k][i]);
        }
        printf("\n");
    }
    printf("\n");
}
	
int lcp(int x, int y) {
    int k, ret = 0;
    if (x == y) return N - x;
    for (k = stp - 1; k >= 0 && x < N && y < N; --k)
        if (P[k][x] == P[k][y])
            x += 1 << k, y += 1 << k, ret += 1 << k;
    return ret;
}

int main() {
    FILE *in = fopen("substr.in", "r");
    fscanf(in, "%d %d\n", &N, &q);
    fgets(A, MAXN, in);
    fclose(in);
    for (i = 0; i < N; ++i)
        P[0][i] = A[i] - 'a';
    for (stp = 1, cnt = 1; cnt >> 1 < N; ++stp, cnt <<= 1) {
        for (i = 0; i < N; ++i) {
            L[i].nr[0] = P[stp - 1][i];
            L[i].nr[1] = i + cnt < N ? P[stp - 1][i + cnt] : -1;
            L[i].p = i;
        }
        sort(L, L + N, cmp);
        for (i = 0; i < N; ++i)
            P[stp][L[i].p] = i > 0 && L[i].nr[0] == L[i - 1].nr[0] && L[i].nr[1] == L[i - 1].nr[1] ? P[stp][L[i - 1].p] : i;
    }
    //print_p();
    int max = 0;
    for(int i = 0; i < N - q; ++i) {
        int prefix = lcp(i, i + q - 1);
        //printf("%d %d: %d\n", i, i + q - 1, prefix);
        if(prefix > max) {
            max = prefix;
        }
    }
    FILE *out = fopen("substr.out", "w");
    fprintf(out, "%d\n", max + 1);
    fclose(out);
    return 0;
}