#include <iostream>
#include <fstream>
#include <algorithm>
#include <cstring>
using namespace std;
const int MAXN=16400;
ifstream si("substr.in");
ofstream so("substr.out");
char s[MAXN];
char *sf[MAXN];
bool cmp(char *a,char *b)
{
    return strcmp(a,b)<0;
}
int main()
{
    int n,k;
    si>>n>>k;
    si>>s;
    for(int i=0;i<n;i++)
    {
        sf[i]=(s+i);
    }
    sort(sf,sf+n,cmp);
    int ans=0;
    for(int i=0;i<n-k+1;i++)
    {
        int sol=0;
        char *sf1,*sf2;
        sf1=sf[i];
        sf2=sf[i+k-1];
        while(*sf1&&*sf2&&*sf1==*sf2)
        {
            sol++;
            sf1++;
            sf2++;
        }
        ans=max(ans,sol);
    }
    so<<ans;
    return 0;
}