https://www.acwing.com/problem/content/submission/4210/

#include <iostream>
#include <stack>
using namespace std;
const int N = 1e6 + 10;
char str[N];
char sta[N];
int hh = 0;
int cnt;

int main()
{
    cin >> str;
    for (int i = 0; str[i]; i ++)
        if(str[i] == '(')  sta[++ hh] = '(';
        else if(hh)  cnt += 2, hh --;
    printf("%d", cnt);
    return 0;

}

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 1000010;

char str[N];

int main()
{
    scanf("%s", str);

    int l = 0, r = 0;
    for (int i = 0; str[i]; i ++ )
        if (str[i] == '(') l ++ ;
        else if (l > 0)
        {
            l -- ;
            r ++ ;
        }

    printf("%d\n", r * 2);
    return 0;
}