import java.util.Scanner;

public class Yuki022 {
	static int N, K;
	static String s;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		N = sc.nextInt();
		K = sc.nextInt() - 1;
		sc.nextLine();
		s = sc.nextLine();
		System.out.println(s.charAt(K) == '(' ? solve('(') : solve(')'));
		sc.close();
	}

	static int solve(char c) {
		int cnt = 1;
		if (c == '(') {
			for (int i = K + 1; i < N; i++) {
				if (s.charAt(i) == c)
					cnt++;
				else
					cnt--;
				if (cnt == 0) {
					return i + 1;
				}
			}
		} else {
			for (int i = K - 1; i >= 0; i--) {
				if (s.charAt(i) == c)
					cnt++;
				else
					cnt--;
				if (cnt == 0) {
					return i + 1;
				}
			}
		}
		return -1;
	}
}