import java.util.Scanner;

public class Main {
	static int N, K;
	
	public static int solve(String ss){
		int buy = 1, eat = 0, atari = 0;
		int i = 0;
		
		while(true){
			eat++;
			if(ss.charAt(i) == '0'){
				i++;
				if(atari > 0){
					atari--;
				}
				else if (eat < K) {
					buy++;
				}
			}
			else if (ss.charAt(i) == '1') {
				i++;
				if (atari > 0) {
					atari--;
				}
			}
			else {
				i++;
				if (atari > 0) {
					atari--;
				}
				atari++;
			}
			
			if(eat >= K)
				break;
		}
		return buy;
	}
	
	public static void main(String[] args){
		Scanner SC = new Scanner(System.in);
		
		N = SC.nextInt();
		K = SC.nextInt();
		String S = SC.next();
		
		String s = "";
		
		for(int i = 0; i < K/N + 2; i++){
			s += S;
		}		
		System.out.println(solve(s));
	}
}