#include <fstream>
#include <unordered_map>
using namespace std;

int baza = 107;
int MOD = 1e9 + 9;

int n, k;
string s;

int put[16401];

void read() {
	ifstream f("substr.in");
	f >> n >> k;
	f >> s;
	f.close();
}

int rez;

unordered_map<int, short> mp;

bool ok(int x) {
	int i, hash = 0;
	mp.clear();
	for (i = 0; i < x; i++)
		hash = (hash + 1LL * put[x - i - 1] * s[i]) % MOD;
	mp[hash]++;
	for (i = x; i < n; i++) {
		hash = (((1LL * hash - 1LL * s[i - x] * put[x - 1] % MOD) * 1LL * baza) % MOD + s[i]) % MOD;
		mp[hash]++;
	}
	for (auto it = mp.begin(); it != mp.end(); it++)
		if (it->second >= k)
			return 1;
	return 0;
}

void solve() {
	int i;
	put[0] = 1;
	for (i = 1; i <= n; i++)
		put[i] = (1LL * put[i - 1] * baza) % MOD;

	int st, dr, mij;
	st = 1, dr = n - 1;
	while (st <= dr) {
		mij = (st + dr) / 2;
		if (ok(mij)) {
			rez = mij;
			st = mij + 1;
		}
		else dr = mij - 1;
	}
}

void output() {
	ofstream g("substr.out");
	g << rez;
	g.close();
}

int main() {
	read();
	solve();
	output();
	return 0;
}