#include <bits/stdc++.h>
#define nm 1<<15

using namespace std;

ifstream fin("substr.in");
ofstream fout("substr.out");

int n,k,i,rez;
char s[nm],*d[nm];

bool cmp(char* a, char* b)
{
    return strcmp(a,b)<0;
}

int main()
{
    int nr;
    fin>>n>>k>>s;

    for(i=0; i<n; ++i)
        d[i]=s+i;

    sort(d,d+n,cmp);

    for(i=0; i<=n-k; ++i)
    {
        nr=0;
        char *a=d[i],*b=d[i+k-1];
        while(*a==*b && *a && *b)
        {
            nr++;
            a++;
            b++;
        }
        rez=max(rez,nr);
    }
    fout<<rez;
    return 0;
}