#include <iostream>
#include <string>

using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    int n, k;
    cin >> n >> k;
    string word;
    cin >> word;
    int sum = 0;
    for (int i = 0; i < k; i++) {
        string subword = word.substr(i * (word.length() / k), word.length() / k);
        int subword_sum = 0;
        int balance = 0;
        for (char c : subword) {
            if (c == '(') {
                balance++;
            }
            else if (c == ')') {
                balance--;
            }
            if (balance < 0) {
                subword_sum++;
                balance = 1;
            }
        }
        subword_sum += balance;
        sum += subword_sum;
    }
    cout << sum << endl;

    return 0;
}