using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(IsValidParentheses("()"));

        Console.WriteLine(IsValidParentheses("((()))"));

        Console.WriteLine(IsValidParentheses("()()()"));

​

        Console.WriteLine(IsValidParentheses("()("));

        Console.WriteLine(IsValidParentheses("((())"));

        Console.WriteLine(IsValidParentheses(")(())("));

    }

    public static bool IsValidParentheses(string s)

    {

        Stack<char> stack = new Stack<char>();

        for(int i = 0; i < s.Length; i++)

        {

            char symb = s[i];

            if (symb == '(') stack.Push(symb);

            if (symb == ')')

            {

                if (stack.Count == 0) return false;

                stack.Pop();

            }

        }

        return stack.Count == 0;

​

    }

}