CSharp Solution

using System;
using System.Collections.Generic;

class Solution
{
    static void Main(String[] args)
    {
        var n = int.Parse(Console.ReadLine());

        Console.WriteLine(factorial(n));
    }

    static int factorial(int n)
    {
        if (n == 1) return 1;

        return factorial(n - 1) * n;
    }
}