#include <fstream>
#include <algorithm>
#include <unordered_map>
#define mod 666013

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

int n,K,st,i,dr,mij,p1[16390],p2[16390],h1,h2,sol,nr,mx,t,k;
struct per{
    int x,y;
}v[16390];
char s[16390];

int caracter(char c){
    if(c>='a' && c<='z')
        return c-'a'+1;
    if(c>='A' && c<='Z')
        return c-'A'+27;
    return c-'0'+53;
}

int cmp(per a, per b){
    if(a.x==b.x)
        return a.y<b.y;
    return a.x<b.x;
}

int main(){
    fin>>n>>K>>(s+1);
    p1[0]=p2[0]=1;
    for(i=1;i<=n;i++){
        p1[i]=(1ll*p1[i-1]*67)%mod;
        p2[i]=(1ll*p2[i-1]*73)%mod;
    }
    st=1,dr=n; sol=0;
    while(st<=dr){
        mij=(st+dr)/2;
        h1=h2=0;
        for(i=1;i<=mij;i++){
            int x=caracter(s[i]);
            h1=(1ll*h1*67+x)%mod;
            h2=(1ll*h2*73+x)%mod;
        }
        v[++t]={h1,h2};
        for(i=mij+1;i<=n;i++){
            int x=caracter(s[i]);
            int c=caracter(s[i-mij]);
            h1=((1ll*h1-1ll*c*p1[mij-1])*67+x)%mod;
            if(h1<0)
                h1+=mod;
            h2=((1ll*h2-1ll*c*p2[mij-1])*73+x)%mod;
            if(h2<0)
                h2+=mod;
            v[++t]={h1,h2};
        }
        sort(v+1,v+t+1,cmp);
        mx=1; bool ok=0; int ct=1;
        int x=v[1].x,y=v[1].y;
        for(i=2;i<=t;i++){
            if(x==v[i].x && y==v[i].y){
                ct++;
                mx=max(mx,ct);
                ok=0;
            }
            else{
                x=v[i].x;
                y=v[i].y;
                ct=1;
            }
        }
        t=0;
        if(mx>=K){
            sol=mij;
            st=mij+1;
        }
        else
            dr=mij-1;
    }
    fout<<sol;
    return 0;
}