import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner scan = new Scanner(System.in)) {
            int n = Integer.parseInt(scan.next());
            int k = Integer.parseInt(scan.next());
            String s = scan.next();
            
            int buy = 0;
            int stack = 0;
            int sum = 0;
            int index = 0;
            
            while(true) {
                
                if(stack == 0) {
                    buy++;
                    sum++;
                } else {
                    stack--;
                }
                
                int now = s.charAt(index) - '0';
                stack += now;
                sum += now;
                if(++index == s.length()) index = 0;
                
                if(sum >= k) break;
            }
            System.out.println(buy);
        }
    }
}