#include <iostream>
#include <string>
using namespace std;

int main() {
	
//	int n = 7;
//	string s = "0121001";

	int n,k;
	string s;
	
	cin >> n >> k ;
	cin >> s;
	
	int sum = 0;
	
	int x = 0;
	int y = 0;
	for(int i = 0; i < n; i++){
		sum += (s[i]-'0');

	}

	
	for(int i =0; i < n; i++){
	
		if(y == 0)x++;
		else y--;
		y =+ (s[i]-'0');	
	}
	
	int np = 0;
	
	if(n <= sum) np = x;
	else{
		
		k -= n;
		x += ( k / n ) * (n - sum);
		k %= n;
	
		for(int i =0; i < k; i++){
			if(y == 0)x++;
			else y--;
			y =+ (s[i]-'0');	
		}
		
		np = x;
	
		
	}
	
		cout << np << endl;
		
		return 0;
}