import java.io.PrintWriter;
import java.util.Scanner;

public class Main{
	public static void main(String[] args) {
		Scanner scanner=new Scanner(System.in);
		PrintWriter out=new PrintWriter(System.out);
		int n=Integer.parseInt(scanner.next());
		int k=Integer.parseInt(scanner.next());
		String s=scanner.next();
		int x=0, y=0;
		int i;
		for(i=0; i<n; i++) {
			int c=s.charAt(i)-'0';
			if(y==0) {
				x++;
			}else {
				y--;
			}
			y+=c;
			if(i+1>=k) {
				out.println(x);
				out.close();
				scanner.close();
				return;
			}
		}
		if(x<=y) {
			out.println(x);
		}else {
			int ans=x+(k-n)/n*(x-y);
			k%=n;
			if(k>0) {
				int y0=y;
				x=0;
				y=0;
				for(i=0; i<n; i++) {
					int c=s.charAt(i)-'0';
					if(y==0) {
						x++;
					}else {
						y--;
					}
					y+=c;
					if(i+1>=k) {
						ans+=Math.max(0,  x-y0);
						break;
					}
				}
			}
			out.println(ans);
		}
		out.close();
		scanner.close();
	}
}