#include <stdio.h>
#include <unordered_map>
#define baza 131
#define mod 666013
using namespace std;
FILE*f=fopen("substr.in","r");
FILE*g=fopen("substr.out","w");
int n,k;
char v[20001];
unordered_map<int, int> h;
int main()
{
	fscanf(f,"%d%d",&n,&k);
	fgets(v+1,n+3,f);
	
	int p=0;
	int u=n;
	
	while(p<=u)
	{
		int ok=0;
		int m=(p+u)/2;
		int b=1;
		int nr=0;
		for(int i=1;i<=m;++i)
		{
			nr+=v[i]*b;
			b*=baza;
		}
		b/=baza;
		h[nr]++;
		if(k==1)
			ok=1;
		for(int i=m+1;!ok&&i<=n;++i)
		{
			nr/=baza;
			nr+=v[i]*b;
			h[nr]++;
			if(h[nr]>=k)
			{
				ok=1;
				break;
			}
		}
		if(ok)
			p=m+1;
		else
			u=m-1;
		h.clear();
	}
	
	fprintf(g,"%d",u);
	
	
	fclose(f);
	fclose(g);
	return 0;
}