#include <fstream>
#include <unordered_map>
#include <string>
#define mod 16385000
using namespace std;

ifstream cin("substr.in");
ofstream cout("substr.out");

int N, K;
string str;

bool isGood(int L) {
	unordered_map<int, int> H;
	int hash = 0;
	int X = 1;
	int A_ = 33;
	for (int i = 0; i < L; i++) {
		hash = ( hash * A_  + str[i]) % mod;
		X = X * A_ % mod;
	}
	
	H[hash] = 1;
	if (K == 1) return true;
	for (int i = L; i < N; i++) {
		hash = ( hash * A_  + str[i]) % mod;
		hash = hash - str[i - L] * X % mod;
		if (hash < 0) hash += mod;
		auto it = H.find(hash);
		if (it != H.end()) {
			it->second++;
			if (it->second >= K) {
				return true;
			}
		} else {
			H[hash] = 1;
		}

	}
	return false;
}

int main()
{
	cin >> N >> K;
	cin >> str;
	int ans = 0;
	for (int step = 1 << 15; step > 0; step >>= 1) {
		if (step + ans <= N && isGood(step + ans)) {
			ans += step;
		}
	}
	cout << ans;
	return 0;
}