#include <iostream>
#include <cstdio>
#include <string>
#include <math.h>
#include <algorithm>

#define MAXN 16384
#define MAXSTEP 20
using namespace std;

int N, k;
char input[MAXN];

struct suffix{
	int firstHalf;
	int secondHalf;
	int poz;

};
suffix L[MAXN];
int P[MAXSTEP][MAXN];
int stp;

bool mycompfunction(const suffix& a, const suffix& b){
	if(a.firstHalf == b.firstHalf)
		return a.secondHalf < b.secondHalf;
	return a.firstHalf < b.firstHalf;
}

void generateSuffixArrays(){

	for(int i = 0; i < N; i++){
		P[0][i] = input[i] - '0';
	}

	for(stp = 1; (1 << stp) <= N; stp ++){
		int length = 1 << (stp - 1);
		for(int i = 0; i < N; i++){
			L[i].poz = i;
			L[i].firstHalf = P[stp - 1][i];
			if(i + length >= N)
				L[i].secondHalf  = -1;
			else
				L[i].secondHalf = P[stp - 1][i + length];

		}
		sort(L, L + N, mycompfunction);
		// actualizeaza P
		for(int i = 0; i < N; i++){
			// same suffix same order number
			if( i > 0 && L[i].firstHalf == L[i-1].firstHalf && L[i].secondHalf == L[i - 1].secondHalf)
				P[stp][L[i].poz] = P[stp][L[i-1].poz];
			else
				P[stp][L[i].poz] = i;
		}
	}

//	for(int i = 0; i < N; i++){
//		printf("%d ", L[i].poz);
//	}

}

int lcp(int x, int y) {
	if (x == y)
		return N - x;
	int res = 0;
	for (int i = stp - 1; i >= 0; i--) {
		if (P[i][x] == P[i][y]) {
			x += 1 << i;
			y += 1 << i;
			res += 1 << i;
		}
	}
	return res;
}

int longestKAppearingSubstring(){
	int maxLength = 0;
	for(int i = 0;  i < N - k; i++){
			int longPref = lcp(L[i].poz, L[i + k - 1].poz);
			maxLength = max(maxLength, longPref);
	}

	return maxLength;
}


int main(){
	freopen("substr.in", "r", stdin);
	freopen("substr.out", "w", stdout);

	scanf("%d %d", &N, &k);
	scanf("%s", input);

//	printf("%d %d %d", '1', 'a', 'A');

	generateSuffixArrays();
	int res = longestKAppearingSubstring();
	printf("%d\n", res);

	return 0;
}