#include <bits/stdc++.h>
using namespace std;

#define MAX_N 16384
#define MAX_LOG 14 // 2^14 = MAX_N
#define BASE 123

int n, k;
char s[MAX_N + 1];
unordered_map<unsigned int, int> freq;

// Maximum number of occurrences of a substring of length len
int maxOccurrences(int len) {
    int i, maxFreq;
    unsigned int curHash, power;

    curHash = 0;
    for (i = 0; i < len; ++i)
        curHash = curHash * BASE + s[i];

    power = 1;
    for (i = 1; i < len; ++i)
        power *= BASE;

    freq.clear();
    freq[curHash] = 1;
    maxFreq = 1;

    for (i = len; i < n; ++i) {
        curHash -= s[i - len] * power; // Remove the first character
        curHash = curHash * BASE + s[i]; // Add the new character

        ++freq[curHash];
        maxFreq = max(maxFreq, freq[curHash]);
    }

    return maxFreq;
}

int longestLength() {
    int len, step;

    len = 0;
    for (step = 1 << MAX_LOG; step > 0; step >>= 1)
        if (len + step <= n && maxOccurrences(len + step) >= k)
            len += step;

    return len;
}

int main() {
    FILE *fin, *fout;
    fin = fopen("substr.in", "r");
    fout = fopen("substr.out", "w");

    fscanf(fin, "%d%d %s", &n, &k, s);
    freq.reserve(n);

    fprintf(fout, "%d\n", longestLength());

    fclose(fin);
    fclose(fout);
    return 0;
}