#include <bits/stdc++.h>
using namespace std;
int n,k,stock,cost;
char box[60];
void f(int rest){
	for(int i=0;i<rest;i++){
		if(stock>0)stock--;else cost++;
		stock+=box[i]-'0';
	}
}
int main(){
    scanf("%d%d%s",&n,&k,box);
	f(min(n,k));
	if(k<n)
        printf("%d",cost);
	else
		if(cost<=stock)
            printf("%d",cost);
		else{
		    cost+=(cost-stock)*(k/n-1);
            f(k%n);
            printf("%d",cost);
        }
    return 0;
}