#include <cstdio>
#include <algorithm>

using namespace std;

const int MAX_N = 17000;

struct suf
{
	int nr[2], p;
} L[MAX_N];

int N, K, P[20][MAX_N], V[MAX_N], stp, Sol;
char S[MAX_N];

void citire()
{
	scanf("%d %d\n", &N, &K);
	fgets(S+1, MAX_N, stdin);
	if(S[N] == '\n') --N;
}

struct cmp
{
	bool operator()(const suf &a, const suf &b) const
	{
		if(a.nr[0] == b.nr[0])
			return a.nr[1] < b.nr[1];
		return a.nr[0] < b.nr[0];
	}
};

int lcp(int x, int y)
{
	if(x == y) return N - x;

	int sol = 0;
	
	for(int k = stp - 1; k && x <= N && y <= N; --k)
		if(P[k][x] == P[k][y])
			sol += (1 << k), x += (1 << k), y += (1 << k);
	return sol;
}

void suffix()
{
	for(int i = 1; i <= N; ++i)
		P[0][i] = S[i];

	int cnt = 1;
	for(stp = 1; (cnt >> 1) <= N; cnt <<= 1, ++stp)
	{
		for(int i = 1; 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+1, L+N+1, cmp());

		for(int i = 1; i <= N; ++i)
			if(i > 1 && L[i].nr[0] == L[i-1].nr[0] && L[i].nr[1] == L[i-1].nr[1])
				P[stp][L[i].p] = P[stp][L[i-1].p];
			else
				P[stp][L[i].p] = i;

//		for(int i = 1; i <= N; ++i)
//			fprintf(stderr, "%d ", L[i].p);
//		fprintf(stderr, "\n");
	}

	for(int i = 1; i <= N; ++i)
	{
//		V[i] = L[i].p;
//		fprintf(stderr, "%d ", V[i]);
	}

	for(int i = 1; i+K-1 <= N; ++i)
		Sol = max(Sol, lcp(L[i].p, L[i+K-1].p));

	printf("%d\n", Sol);
}

int main()
{
	freopen("substr.in","rt",stdin);
	freopen("substr.out","wt",stdout);

	citire();
	suffix();
}