# include <algorithm>
# include <cstdio>
# include <cstring>

bool comp (char *a, char *b) {
    return strcmp (a, b) < 0;
}

const char *FIN = "substr.in", *FOU = "substr.out";
const int MAX = 16385;

char T[MAX], *it[MAX];
int N, K, sol;

int main (void) {
    fscanf (fopen (FIN, "r"), "%d %d %s", &N, &K, T);
    for (int i = 0; i < N; ++i)
        it[i] = T + i;
    std :: sort (it, it + N, comp);
    for (int i = 0; i < N - K + 1; ++i) {
        int maxi = 0;
        for (char *a = it[i], *b = it[i + K - 1]; *a == *b && *a && *b; ++maxi, ++a, ++b);
        sol = std :: max (sol, maxi);
    }
    fprintf (fopen (FOU, "w"), "%d", sol);
}