#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;
const int64_t MOD = 1e9 + 7;

int N, K;

int searchA(string S) {
	//cout << "A" << endl;
	vector<char> v;

	for (int i = 0; i < N; i++) {
		char ch = S.at(i);

		if ((ch == '(') || (ch == '{')) {
			v.push_back(ch);
		}
		else {
			if (v.at(v.size() - 1) == '{') {
				return i + 1;
			}
			else {
				v.pop_back();
			}
		}
	}
	
	return -1;
}

int searchB(string S) {
	//cout << "B" << endl;
	vector<char> v;

	for (int i = S.size()-1; i >=0; i--) {
		char ch = S.at(i);

		if ((ch == ')') || (ch == '}')) {
			v.push_back(ch);
		}
		else {
			if (v.at(v.size() - 1) == '}') {
				return i + 1;
			}
			else {
				v.pop_back();
			}
		}
	}
	
	return -1;
}

int main() {
	string S;
	cin >> N >> K >> S;

	vector<char> v;

	char &ch = S.at(K - 1);
	if (ch == '(') {
		ch = '{';
		cout << searchA(S) << endl;
	}
	else {
		ch = '}';
		cout << searchB(S) << endl;
	}
}