using System;

public class Program

{

    public static void Main()

    {

        Console.Write("Enter a positive integer: ");

​

        int num;

        if(int.TryParse(Console.ReadLine(), out num)&& num>0){

        int fact = num;

        while(num>1){

            fact*=num-1;

            num--;

        }

        Console.Write("Factorial: "+fact);

    }else{

            Console.Write("Invalid");

        }

           }

}