import java.util.Scanner;
 
public class Main {
	public static void main(String[] args) {
		Main p = new Main();
	}
 
	public Main() {
		Scanner sc = new Scanner(System.in);
		sc.nextInt();
		int n = sc.nextInt()-1;
		String s =sc.next();
 
		System.out.println(solve(s, n)+1);
	}
 
	public int solve(String s, int n) {
		int c = 0;
		if(s.charAt(n)=='('){
			for(int i=n;i<s.length();i++){
				if(s.charAt(i)=='(')
					c--;
				else
					c++;
				if(c==0)
					return i;
			}
		}else{
			for(int i=n;0<=i;i--){
				if(s.charAt(i)==')')
					c--;
				else
					c++;
				if(c==0)
					return i;
			}
		}
 
		return -1;
	}
}