#include <fstream>
#include <algorithm>
#define v1 first.first
#define v2 first.second
#define poz second
#define DIM 16400
using namespace std;
char s[DIM];

pair< pair<int, int>, int > L[DIM];
int p[17][DIM], v[DIM] ;

int n, k, i, e, len;

int lcp(int i, int j) {
    int f = e;
    int putere = (1 << e);
    int sol = 0;
    while (putere) {
        if (p[f][i] == p[f][j]) {
            sol += putere;
            i+=putere;
            j+=putere;
        }

        f--;
        putere /= 2;
    }
    return sol;
}

int main() {
    ifstream fin ("substr.in");
    ofstream fout("substr.out");
    fin>>n>>k;
    fin>>s;

    for (i=0;i<n;i++)
        p[0][i] = s[i] - '0';

    for (e=0, len = 1; len <= n; e++, len*=2) {
        /// am sortat dupa prefixe de lungime len = 2^e
        /// si construiesc linia e+1 adica sortat dupa prefixe de lungime 2*len
        for (i=0;i<n;i++) {
            L[i].v1 = p[e][i];
            if (i+len < n)
                L[i].v2 = p[e][i+len];
            else
                L[i].v2 = -1;
            L[i].poz = i;
        }

        sort(L, L+n);

        p[e+1][ L[0].poz ] = 0;
        for (i=1;i<n;i++)
            if (L[i].v1 == L[i-1].v1 && L[i].v2 == L[i-1].v2)
                p[e+1][ L[i].poz ] = p[e+1][ L[i-1].poz ];
            else
                p[e+1][ L[i].poz ] = p[e+1][ L[i-1].poz ] + 1;
    }

    for (i=0;i<n;i++) {
        v[ p[e][i] ] = i;
    }

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

    }
/*
    for (i=0;i<n;i++)
        fout<<v[i]<<" ";
*/

    fout<<sol;
}