#include <stdio.h>
#define baza 131
#define mod 666013
using namespace std;
FILE*f=fopen("substr.in","r");
FILE*g=fopen("substr.out","w");
int n,k,viz[20001];;
char v[20001];
int h[mod+3];
int main()
{
    fscanf(f,"%d%d\n",&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;
            nr%=mod;
            b*=baza;
            b%=mod;
        }
        b/=baza;
        h[nr%mod]++;
        int nr1=0;
        viz[++nr1]=nr%mod;
        if(k==1)
            ok=1;
        for(int i=m+1;!ok&&i<=n;++i)
        {
            nr/=baza;
            nr+=v[i]*b;
            nr%=mod;
            h[nr]++;
             viz[++nr1]=nr;
            if(h[nr]>=k)
            {
                ok=1;
                break;
            }
        }
        if(ok)
            p=m+1;
        else
            u=m-1;
        for(int i=1;i<=nr1;++i)
            h[viz[i]]=0;
    }

    fprintf(g,"%d",u);


    fclose(f);
    fclose(g);
    return 0;
}