#include<stdio.h>
#include<algorithm>

using namespace std;

const char IN[] = "substr.in";
const char OUT[] = "substr.out";
const int NMAX = 16985;
const int LGMAX = 20;

struct S{
    int c1 , c2 , act;
} X[NMAX];

char A[NMAX];
int SA[LGMAX][NMAX] , N , K , pas , REZ , cnt ;

int sort_comp(S a , S b)
{
    if(a.c1 == b.c1) return a.c2 < b.c2;
    else return a.c1 < b.c1;
    }

int LCP(int x ,int y)
{
    int k , l = 0;
    if(x == y) return N - x + 1;
    for( k = pas - 1 ; k >= 0 && x <= N && y <= N ; --k)
     if(SA[k][x] == SA[k][y])
      x += (1<<k) , y += (1<<k) , l += (1<<k) ; 
    return l;
    }    

int main()
{
    freopen(IN  , "r" , stdin);
    freopen(OUT , "w" , stdout);
    
    scanf("%d %d\n" , &N , &K);
    gets(A);
    for(int i = 0 ; i < N ; ++i)
     SA[0][i] = A[i] - '0';
    
    for( pas = 1 , cnt = 1 ; ( cnt >> 1 ) < N ; cnt <<= 1 , ++pas)
     {
            for(int i = 0 ; i < N ; ++i)
            {
                X[i].c1 = SA[pas - 1][i];
                X[i].c2 = (i + cnt < N ) ? SA[pas - 1][i + cnt] : -1;
                X[i].act = i;            
                } 
             sort(X , X + N , sort_comp);   
             for(int i = 0 ; i < N ; ++i)
              if(i > 0 && X[i].c1 == X[i - 1].c1 && X[i].c2 == X[i - 1].c2) SA[pas][X[i].act] = SA[pas ][X[i - 1].act];
              else SA[pas][X[i].act] = i;
        }
    for(int i = 0 ; i + K < N ; ++i)
     {
            int temp = LCP (X[i].act , X[i + K - 1].act);
            if(temp > REZ) REZ = temp;
            }    
    printf("%d\n",REZ);        
    return 0;
}