Product Sign Of 3 Numbers Without Calculation

using System;
class ProductSignOf3NumsWithoutCalculation
{
  static void Main()
  {
//Telerik Academy
    //Write a program that shows the sign (+ or -) of the product of three real numbers without calculating it. Use a sequence of if statements.

    Console.Write("Please enter the first number:");
    decimal firstNum = decimal.Parse(Console.ReadLine());
    Console.Write("Please enter the second number:");
    decimal secondNum = decimal.Parse(Console.ReadLine());
    Console.Write("Please enter the third number:");
    decimal thirdNum = decimal.Parse(Console.ReadLine());

    if (firstNum == 0 || secondNum == 0 || thirdNum == 0)
    {
      Console.WriteLine("At least one of the entered numbers is zero so the product of the numbers will be 0!");
    }
    else if ((firstNum > 0 && secondNum > 0 && thirdNum > 0) || (firstNum > 0 && secondNum < 0 && thirdNum < 0) || (firstNum < 0 && secondNum < 0 && thirdNum > 0) || (firstNum < 0 && secondNum >0 && thirdNum < 0))
    {
      Console.WriteLine("The sign of the product of the three numbers: ({0}) * ({1}) * ({2}) is PLUS (+)!", firstNum, secondNum, thirdNum);
    }
    else
    {
      Console.WriteLine("The sign of the product of the three numbers: ({0}) * ({1}) * ({2}) is MINUS (-)!", firstNum, secondNum, thirdNum);
    }
  }
}