using System;

public class Program

{

    public static void Main()

    {

        var str = "2 * (3.4 - (-7)/2)*(a-2)/(b-1)))";

        Console.WriteLine($"string {str} valid: {IsValid(str)}");

    }

    public static bool IsValid(string s)

    {

        var count = 0;

        foreach (var c in s)

        {

            if (c == '(')

                count++;

            if (c == ')')

            {

                if (count == 0) return false;

                count--;

            }

        }

        return count == 0;

    }

}