#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;

ifstream F("substr.in");
ofstream G("substr.out");

const int N = 100010;

int n,k,dp[20][N],ln,p[N];
char a[N];

struct trio { int a,b,p; } t[N];

bool cmpt(trio a,trio b)
{
    return a.a < b.a || ( a.a == b.a && a.b < b.b );
}

bool cmp(int x,int y)
{
    return dp[ln][x] < dp[ln][y];
}

void build()
{
    for (int i=1;i<=n;++i)
        dp[0][i] = a[i]-'0';
    for (int i=1;(1<<i)<=n*2;++i)
    {
        for (int j=1;j<=n;++j)
        {
            t[j].a = dp[i-1][j];
            t[j].b = j+(1<<i)/2 <= n ? dp[i-1][j+(1<<i)/2] : 0;
            t[j].p = j;
        }
        sort(t+1,t+n+1,cmpt);
        for (int j=1;j<=n;++j)
        {
            dp[i][t[j].p] = j;
            if ( t[j].a == t[j-1].a && t[j].b == t[j-1].b )
                dp[i][t[j].p] = dp[i][t[j-1].p];
        }
        ln = max(ln,i);
    }
}



int lcp(int x,int y)
{
    int ans = 0;
    for (int i=ln;i>0 && x<=n && y<=n;--i)
        if ( dp[i][x] == dp[i][y] )
        {
            ans += 1<<i;
            x += 1<<i;
            y += 1<<i;
        }
    return ans;
}

int main()
{
    F>>n>>k;
    F>>(a+1);

    build();

    for (int i=1;i<=n;++i)
        p[i] = i;
    sort(p+1,p+n+1,cmp);

    int ans = 0;
    for (int i=k,j=1;i<=n;++i,++j)
        ans = max(ans,lcp(p[j],p[i]));
    G<<ans<<'\n';
}