#include<fstream>
#include<algorithm>
#define x first.first
#define y first.second
#define z second
#define DIM 16400
using namespace std;
ifstream fin("substr.in");
ofstream fout("substr.out");
int n,k,h,lung,nr;
int a[17][16400],v[16400];
char s[16400];
pair< pair<int,int>,int> L[16400];

int LCP(int i,int j) {
    int E=h;
    int pow= 1<<h;
    int sol=0;
    while(pow!=0){
        if(a[E][i]==a[E][j]) {
            sol+=pow;
            i+=pow;
            j+=pow;
        }
        E--;pow/=2;
    }
    return sol;
}

int main(){
    fin>>n>>k;
    fin>>s;
    for(int i=0;i<n;i++)
        a[0][i]=s[i]-'0';

    /// PRIMA LINIE

    for(h=0,lung=1; lung<=n ; h++,lung*=2){
        for(int i=0;i<n;i++){
            L[i].x=a[h][i];
            if(i+lung<n)
                L[i].y=a[h][i+lung];
            else
                L[i].y=-1;
            L[i].z=i;
        }
        sort(L,L+n);
        a[h+1][L[0].z]=0;
        for(int i=1;i<n;i++)
            if(L[i].x==L[i-1].x && L[i].y==L[i-1].y)
                a[h+1][L[i].z]=a[h+1][L[i-1].z];
            else
                a[h+1][L[i].z]=a[h+1][L[i-1].z]+1;
    }

    /// PREFIXE SORTATE

    for(int i=0;i<n;i++)
        v[a[h][i]]=i;

    for(int i=0;i+k-1<n;i++) {
        nr=max(nr, LCP(v[i],v[i+k-1]) );
    }

    fout<<nr;
    return 0;
}