#include <bits/stdc++.h>
using namespace std;

signed main(){
  int N, K; cin >> N >> K;
  string S; cin >> S;
  vector< int > vis( N );
  for( int i = 0, c = 0, b = 0, e = 0; ; i = ( i + 1 ) % N ){
    if( vis[ i ] ){
      vector< int > vis2( N );
      for( int j = i, x = 0, y = 0, z = 0; ; j = ( j + 1 ) % N ){
        if( vis2[ j ] ){
          b += ( K - z ) / z * y;
          e += ( K - z ) / z * z;
          break;
        }
        vis2[ j ] = 1;
        if( e + z >= K )
          cout << b + y << endl, exit( 0 );
        ++y, ++z, x += S[ j ] - '0';
        for( int k = ( j + 1 ) % N; ; k = ( k + 1 ) % N ){
          if( x == 0 ){
            j = k - 1;
            break;
          }
          if( j == k )
            cout << b + y << endl, exit( 0 );
          --x;
          x += S[ k ] - '0';
          ++z;
        }
      }
    }
    vis[ i ] = 1;
    if( e >= K )
      cout << b << endl, exit( 0 );
    ++b, ++e, c += S[ i ] - '0';
    for( int j = ( i + 1 ) % N; ; j = ( j + 1 ) % N ){
      if( c == 0 ){
        i = j - 1;
        break;
      }
      if( i == j )
        cout << b << endl, exit( 0 );
      --c;
      c += S[ j ] - '0';
      ++e;
    }
    if( e >= K )
      cout << b << endl, exit( 0 );
  }
  return 0;
}