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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,K; cin >> N >> K;
    string s; cin >> s;
    
    vector<int> buy(N+1);
    
    int bring = 0,answer = 0,sum = 0;
    for(int i=0; i<min(N,K); i++){
        if(bring == 0) bring++,answer++;
        bring--,bring += s.at(i)-'0',sum += s.at(i)-'0';
        buy.at(answer) = i+1;
    }
    for(int i=answer+1; i<=N; i++) buy.at(i) = N;
    K -= N;
    if(K <= 0 || sum >= N){cout << answer << endl; return 0;}

    answer += (N-sum)*((K-1)/N),K %= N;
    if(K == 0) K = N;
    for(int i=0; ; i++) if(buy.at(i+bring) >= K){cout << answer+i << endl; break;}
}