#include <iostream>
using namespace std;

int solve(int N, int K, string S){
    int used = 0, remain = 0;
    
    for(int i=0;i<N;i++){
        if(remain > 0){
            --remain;
        } else {
            ++used;
        }
        
        --K;
        if(K <= 0)return used;
    
        remain += S[i] - '0';
    }
    
    if(remain >= used)return used;
    
    int res = used;
    int t = max(K / N - 1000, 0);
    K -= N * t;
    res += (used - remain) * t;
    
    for(int i=0;;i++){
        if(remain > 0){
            --remain;
        } else {
            ++res;
        }
        
        --K;
        if(K <= 0)return res;
        
        remain +=  S[i % N] - '0';
    }

}

int main(){
    int N, K;
    string S;
    
    cin >> N >> K >> S;
    cout << solve(N, K, S) << endl;
    
    return 0;
}