#include <stdio.h>
#include <algorithm>
using namespace std;
#define NMAX 17000
struct xyp{
	int x, y, p;};
struct comp{
	bool operator()(const xyp &a, const xyp &b){
		if(a.x == b.x) return a.y < b.y;
		return a.x < b.x;
	}
};
xyp P[NMAX];
char S[NMAX];
int A[16][NMAX];
int n, k;
int lcp(int x, int y){
	int step = 0;
	for(; (1<<step) <= n; ++step); --step;
	int sol = 0;
	for(int j = step; j >= 0; --j)
		if(x + (1<<j) -1 <= n && y + (1<<j) -1 <= n && A[j][x] == A[j][y])
			sol += (1<<j), x += (1<<j), y += (1<<j);
	return sol;
}
void suffix_array(){
	for(int i = 1; i <= n; ++i)
		A[0][i] = S[i] -'a';
	int lung = 0;
	for(int j = 1; (1<<(j-1)) <= n; ++j){
		lung = j;
		for(int i = 1; i <= n; ++i){
			P[i].x = A[j-1][i];
			P[i].y = i + (1<<(j-1)) > n ? -1 : A[j-1][i+(1<<(j-1))];
			P[i].p = i;
		}
		int p = 0;
		sort( P + 1, P + n + 1, comp());
		for(int i = 1; i <= n; ++i)
			if(i > 1 && P[i-1].x == P[i].x && P[i-1].y == P[i].y)
				A[j][P[i].p] = p;
			else A[j][P[i].p] = ++p;
	}
}
int main(){
	freopen("substr.in", "r", stdin);
	freopen("substr.out" ,"w", stdout);
	scanf("%d%d\n", &n, &k);
	fgets(S + 1, NMAX, stdin);
	
	suffix_array();
	
	int sol = 0;
	for(int i = 1; i <= n-k+1; ++i)
		sol = max(lcp(P[i].p, P[i+k-1].p), sol);
	printf("%d\n", sol);
	
	return 0;
}