#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

#define DxBG
#define FL

#define fin  "substr.in"
#define fout "substr.out"

#define mp make_pair
#define pb push_back
#define f first
#define s second

const int Nmax  = 17000;
const int LgMax = 20;

int N,K,best,lim,P[LgMax][Nmax];
char buff[Nmax];
vector < pair < pair <int,int> ,int> > v;

int lcp(int x,int y)
{
	int step,cnt = 0;
	if ( x == y ) return N - x;
	for ( step = lim; step >= 0 && x < N && y < N; --step )
	{
		if ( P[step][x] == P[step][y] )
			cnt += 1 << step, x += 1 << step, y += 1 << step;
#ifdef DBG
		printf("%d %d %d\n",cnt,x,y);
#endif
	}
#ifdef DBG
	printf("--\n");
#endif
	return cnt;
}

void readdata_solve()
{
	int i,step,cnt;
#ifdef FL
	freopen(fin,"r",stdin);
	freopen(fout,"w",stdout);
#endif
	scanf("%d%d\n",&N,&K);
	fgets(buff,Nmax,stdin);

	for ( i = 0; i < N; ++i )
		P[0][i]=buff[i]-'a';
//build suffarray
	for ( step = 1, cnt = 1; cnt <= N; cnt <<= 1, ++step )
	{
		v.clear();
		for ( i = 0; i < N; ++i )
			v.pb(mp(mp(P[step-1][i],(i+cnt<N)?(P[step-1][i+cnt]):(-1)),i));
		sort(v.begin(),v.end());
		for ( i = 0; i < N; ++i )
			P[step][v[i].s] = ( i > 0 && v[i].f.f == v[i-1].f.f && v[i].f.s == v[i-1].f.s ) ? ( P[step][v[i-1].s] ) : ( i );
	}

	lim = step - 1;
#ifdef DBG
	for ( step = 0; step <= lim; ++step,printf("\n") )
	for (  i   = 0; i < N; ++i )
		printf("%d ",P[step][i]);
#endif

//query lcp
	for ( i = 0; i + K - 1 < N; ++i )
		best = max(best,lcp(v[i].s,v[i+K-1].s));

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

int main()
{
	readdata_solve();
	return 0;
}