Regular Bracket Sequence

string s;
    cin >> s;
    int c_r = 0, c_t = 0;
    for (int i = 0; i < s.size(); i++)
    {
        if (s[i] == '(')
        {
            c_r++;
        }
        else if (s[i] == ')' && c_r != 0)
        {
            c_t++;
            c_r--;
        }
    }
    cout << c_t * 2;