import java.util.Scanner;

public class No022_SupprotBrackets {

	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();	// 文字数
        int b = sc.nextInt();	// 対象番号
        String s = sc.next();	// 文字列

        final String LB = "(";
        final String RB = ")";

        int cnt = 0;

        if (LB.equals(s.substring(b-1,b))) {
	        for (int i=b; i<a; i++) {
	        	if (LB.equals(s.substring(i, i+1))) cnt++;
	        	if (RB.equals(s.substring(i, i+1))) cnt--;
	        	if (cnt < 0) {
	        		System.out.println(i+1);
	        		break;
	        	}
	        }
        } else {
	        for (int i=b; i>0; i--) {
	        	if (LB.equals(s.substring(i-1, i))) cnt--;
	        	if (RB.equals(s.substring(i-1, i))) cnt++;
	        	if (cnt <= 0) {
	        		System.out.println(i);
	        		break;
	        	}
	        }
        }
	}

}