#include <stdio.h>
#include <map>
#define baza 131
#define mod 9500041
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];
long long X,Y;
void euclid(int a,int b,long long &x,long long &y){
    if(!b){
        x=1;
        y=0;
        return ;
    }else{
        long long  x0,y0;
        euclid(b,a%b,x0,y0);
        x=y0;
        y=x0-(a/b)*y0;
    }

}
long long  invers(int a)
{
    X=Y=0;
    euclid(a,mod,X,Y);
    while(X<=0)
        X=mod+X%mod;

    return X;
}
int main()
{
    fscanf(f,"%d%d\n",&n,&k);
    fgets(v+1,n+3,f);

    int p=0;
    int u=n;
    int BAZA=invers(baza);
    while(p<=u)
    {
        int ok=0;
        int m=(p+u)/2;
        int b=1;
        long long nr=0;
        nr=v[1];
        for(int i=2;i<=m;++i)
        {
            b*=baza;
            b%=mod;
            nr+=v[i]*b;
            nr%=mod;

        }

        h[nr]++;
        int nr1=0;
        viz[++nr1]=nr;
        if(k==1)
            ok=1;
        for(int i=m+1;!ok&&i<=n;++i)
        {
            nr+=mod-v[i-m];
            nr%=mod;
            nr*=BAZA;
            nr%=mod;
            nr+=v[i]*b;
            nr%=mod;
            h[nr]++;
            viz[++nr1]=nr;
            if(h[nr]>=k)
            {
                ok=1;

            }
        }
        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;
}