import java.util.Scanner;


public class Main {
	public static void main(String[] a) {
		Scanner s=new Scanner(System.in);
		s.nextInt();
		int K=s.nextInt()-1,i,D,L=1;
		String P=s.next();
		D=81-2*P.charAt(K);
		for(i=K+D;0!=(L+=D*(81-2*P.charAt(i)));i+=D);
		System.out.println(i+1);
	}
}