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

int main() {
    int n,k;string s;
    cin>>n>>k>>s;
    int buy=0,stock=0;
    for (int i=0;i<n;i++) {
        if (stock>0) stock--;
        else buy++;
        k--;
        if (k==0) {
            cout<<buy<<endl;
            return 0;
        }
        stock+=s[i]-'0';
    }
    if (buy<=stock) {
        cout<<buy<<endl;
        return 0;
    }
    int buyperbox=buy-stock;
    buy+=k/n*buyperbox;
    k%=n;
    for (int i=0;i<k;i++) {
        if (stock>0) stock--;
        else buy++;
        stock+=s[i]-'0';
    }
    cout<<buy<<endl;
    return 0;
}