#include <iostream>
#include <algorithm>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
//#define endl "\n";
ll N, A;
string S;

int main(){
  cin >> N >> A;
  cin >> S;
  //1周目
  ll pos = 1200;
  ll cnt = 0;
  for(int i = 0; i < N; i++){
    if(S[i] == '0'){
      pos -= 1;
    }else{
      if(pos < 1200){
        pos++;
        cnt++;
        if(A == cnt){
          cout << i + 1 << endl;
          return 0;
        }
      }
    }
  }
  //2周目
  A -= cnt; //残り
  ll ans = N;
  ll tmppos = pos;
  ll loopcnt = 0;
  for(int i = 0; i < N; i++){
    if(S[i] == '0'){
      tmppos -= 1;
    }else{
      if(tmppos < 1200){
        tmppos++;
        loopcnt++;
      }
    }
  }
  ans += ((A - 1) / loopcnt) * N;
  A -= ((A - 1) / loopcnt) * loopcnt;
  //残りを計算
  for(int i = 0; i < N; i++){
    ans++;
    if(S[i] == '0'){
      pos -= 1;
    }else{
      if(pos < 1200){
        pos++;
        A--;
        if(A <= 0){
          cout << ans << endl;
          return 0;
        }
      }
    }
  }
  return 0;
}