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

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

  stack<int> s;
  int ans = 0;
  for (int i = 0; i < N; ++i) {
    int flag = -1;
    if (!s.empty())
      flag = s.top();

    if (flag == K - 1 && S[i] == ')')
      ans = i + 1;
    if (i == K - 1 && S[i] == ')')
      ans = s.top() + 1;

    if (S[i] == '(')
      s.push(i);
    else
      s.pop();
  }

  cout << ans << endl;
}