#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

int main()
{
	int n, k; cin >> n >> k;
	k--;
	string s; cin >> s;

	int ans = -1;
	if (s[k] == '(') {
		int cnt = 0;
		for (int i = k; i < n; i++) {
			if (s[i] == ')')cnt--;
			else cnt++;

			if (cnt == 0) {
				ans = i + 1;
				break;
			}
		}
	}
	else {
		int cnt = 0;
		for (int i = k; i >= 0; i--) {
			if (s[i] == ')')cnt++;
			else cnt--;

			if (cnt == 0) {
				ans = i + 1;
				break;
			}
		}
	}

	cout << ans << endl;

    return 0;
}