# include <fstream>
# include <string>
# include <map>
# define DIM 16484
# define PRAG 10000000
#define MOD1 100007
#define MOD2 100021
using namespace std;
ifstream fin("substr.in");
ofstream fout("substr.out");
char ch[DIM];
map<long long,int> m;
int n,k,step,i,j,h1,h2,p=73,p1,p2,r1,r2;
int el(char ch){
    if(ch>='0'&&ch<='9')
        return 53+ch-'0';
    if(ch>='a'&&ch<='z')
        return ch-'a'+1;
    if(ch>='A'&&ch<='Z')
        return ch-'A'+27;
}
bool val(int q){
    p1=p2=1;
    for(i=1;i<=q;i++){
        h1=(p*h1+el(ch[i]))%MOD1;
        h2=(p*h2+el(ch[i]))%MOD2;
        if(i!=1){
            p1*=p;
            p2*=p;
            p1%=MOD1;
            p2%=MOD2;
        }
    }
    if(!m.count(1LL*h1*PRAG+h2))
        m[1LL*h1*PRAG+h2]=1;
    else
        m[1LL*h1*PRAG+h2]++;
    if(m[1LL*h1*PRAG+h2]==k){
        m.clear();
        h1=h2=0;
        p1=p2=1;
        return 1;
    }
    for(i=q+1;i<=n;i++){
        r1=p1*el(ch[i-q])%MOD1;
        r2=p2*el(ch[i-q])%MOD2;
        h1-=r1;
        if(h1<0)
            h1+=MOD1;
        h2-=r2;
        if(h2<0)
            h2+=MOD2;
        h1=(h1*p+el(ch[i]))%MOD1;
        h2=(h2*p+el(ch[i]))%MOD2;
        if(!m.count(1LL*h1*PRAG+h2))
            m[1LL*h1*PRAG+h2]=1;
        else
            m[1LL*h1*PRAG+h2]++;
        if(m[1LL*h1*PRAG+h2]==k){
            m.clear();
            h1=h2=0;
            p1=p2=1;
            return 1;
        }
    }
    h1=h2=0;
    p1=p2=1;
    m.clear();
    return 0;
}
int sol(){
    for(step=1;step<=n;step*=2);
    for(j=0;step;step/=2)
        if(j+step<=n&&val(j+step))
            j+=step;
    return j;
}
int main () {
    fin>>n>>k>>ch+1;
    fout<<sol();
    return 0;
}