#include<fstream>
#include<iostream>
#include<cstring>
#include<algorithm>
#define v1 first.first
#define v2 first.second
#define s second
#define mod 1000000007
using namespace std;
ifstream fin("substr.in");
ofstream fout("substr.out");
int b,p,n,k,sol,i,v[20][16400],nr,f[16400];
pair<pair<int,int>,int> d[16400];
char c[16400];
int lca(int i, int j)
{
    int val=(1<<p),h=p,st=0;
    while(val)
    {
        if(v[h][i]==v[h][j])
            st+=val,i+=val,j+=val;
        h--;val/=2;
    }
    return st;
}
int main()
{
    fin>>n>>k;
    if(k==1){fout<<n;return 0;}
    fin>>c;
    for(i=1;i<=n;i++)
        v[0][i]=c[i-1]-'0';
    for(p=0,b=1;b<=n;p++,b<<=1)
    {
        for(i=1;i<=n;i++)
        {
            d[i].v1=v[p][i];
            if(i+b>n) d[i].v2=-1;
            else d[i].v2=v[p][i+b];
            d[i].s=i;
        }
        sort(d+1, d+n+1);nr=-1;
        for(i=1;i<=n;i++)
        {
            if(i!=-1&&d[i].v1==d[i-1].v1&&d[i].v2==d[i-1].v2) v[p+1][d[i].s]=v[p+1][d[i-1].s];
            else v[p+1][d[i].s]=++nr;
        }
    }
    for(i=1;i<=n;i++)
        f[v[p][i]+1]=i;
    for(i=1;i+k-1<=n;i++)
        sol=max(sol, lca(f[i], f[i+k-1]));
    fout<<sol;
    return 0;
}