import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;

public class No22 {

	public static void main(String[] args) throws IOException {
		//括弧の対応
		String[] text = readStr();
		int N = Integer.parseInt(text[0].split(" ")[0]) , K = Integer.parseInt(text[0].split(" ")[1]) , r = 0;
		String S = text[1];
		Deque<Integer> dq = new ArrayDeque<>();
		
		for(int i = 0;i < N;i++) {
			if(S.charAt(i) == '(') {
				dq.push(i+1);
			}else {
				r = dq.pop();
				if(i+1 == K || r == K) {
					r = i + 1 + r - K;
					break;
				}
			}
		}
		System.out.println(r);
		

	}
	
	public static String[] readStr() throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		ArrayList<String> list = new ArrayList<>();

		do {
			list.add(br.readLine());
		}while(br.ready());

		br.close();

		String[] text = new String[list.size()];
		list.toArray(text);

		return text;

	}

}