using System;

using System.Text;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(BalanceString("())(()"));

        Console.WriteLine(BalanceString("abcd("));

        Console.WriteLine(BalanceString("(abcd)"));

        Console.WriteLine(BalanceString(")a(((bc))d("));

        Console.WriteLine(BalanceString("((())(()"));

        Console.WriteLine(BalanceString("a(b)c)d(e(f)g"));

        Console.WriteLine(BalanceString("a(b)c)"));

    }

    public static string BalanceString(string s) {

        var count = 0;

        var arr = s.ToCharArray();

        for (var i = 0; i < arr.Length; ++i) {

            var c = arr[i];

            if (c == '(') {

                count++;

            } else if (c == ')') {

                if (count == 0) {

                    arr[i] = '\0';

                } else {

                    count--;

                }

            }

        }

        count = 0;

        for (var i = arr.Length - 1; i >= 0; --i) {

            var c = arr[i];

            if (c == '\0') continue;

            if (c == ')') {

                count++;

            } else if (c == '(') {

                if (count == 0) {

                    arr[i] = '\0';

                } else {

                    count--;

                }

            }

        }

​

        var sb = new StringBuilder();

        for (var i = 0; i < arr.Length; ++i) {

            if (arr[i] != '\0') sb.Append(arr[i]);

        }

        return sb.ToString();

    }

}