// https://szkopul.edu.pl/problemset/problem/KlznBqTfieN-sWvUfTD0BJdT/site/?key=statement

#include <iostream>

constexpr int sizik = 1000 * 1001;

int pref[sizik];

int main() {
    std::ios_base::sync_with_stdio(0);
    std::cin.tie(0);
    std::cout.tie(0);

    int n, H;
    std::cin >> n >> H;

    for (int i = 1; i <= n; i++) {
        char c;
        std::cin >> c;

        if (c == '(') {
            pref[i]++;
        } else {
            pref[i]--;
        }

        pref[i] += pref[i - 1];
    }

    int balans = 0;
    int ans = 0;

    for (int i = 1; i <= n; i++) {
        if (pref[i] + balans > H) {
            ans += 2;
            balans -= 2;
        } else if (pref[i] + balans < 0) {
            balans += 2;
        }
    }

    std::cout << ans << '\n';

    return 0;
}