Factorial

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Factorial
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = System.Numerics.BigInteger.Parse(Console.ReadLine());

            Console.WriteLine(Factorial(input));
        }

        static System.Numerics.BigInteger Factorial(System.Numerics.BigInteger num)
        {
            if (num == 0) return 1;
            else return num * Factorial(num - 1);
        }
    }
}