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

int N,A;

signed main(){
  cin>>N>>A;
  string S; cin>>S;
  vector<bool> B(N);
  for(int i = 0; i < N; i++) B[i] = (S[i] == '1');
  int now = 1200;
  int cnt = 0;
  for(int i = 0; i < N; i++){
  	if(B[i]){
  		if(1200 > now){
  			now++;
  			cnt++;
  		}
  	}
  	else now--;
  	if(A <= cnt){
  		cout << i+1 << "\n";
  		return 0;
  	}
  }
  int a = now;
  int b = cnt;
  cnt = 0;
  for(int i = 0; i < N; i++){
  	if(B[i]){
  		if(1200 > now){
  			now++;
  			cnt++;
  		}
  	}
  	else now--;
  }
  A -= b;
  int ans = N;
  A--;
  ans += (A / cnt) * N;
  A %= cnt;
  A++;
  for(int i = 0; i < 2*N; i++){
  	if(A <= 0){
  		cout << ans + i << "\n";
  		return 0;
  	}
  	if(B[i]){
  		if(1200 > now){
  			now++;
  			cnt++;
  			A--;
  		}
  	}
  	else now--;
  	if(A <= 0){
  		cout << ans + i + 1 << "\n";
  		return 0;
  	}
  }
}