Catalan Numbers

using System;
using System.Numerics;

class Program
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        if (n < 1)
        {
            Console.WriteLine("Invalid input,Please input N bigger or equal to 1!");
        }
        else
        {
            BigInteger factoriel = 1;
            int temp = n+1;
            int temp2 = n;
            for (int i = 2*n; i > 1; i--)
            {
                factoriel *= i;
                if (temp==i)
                {
                    factoriel /= temp;
                    temp--;
                }
                if (temp2 == i)
                {
                    factoriel /= temp2;
                    temp2--;
                }
            }
            Console.WriteLine(factoriel);
        }

    }
}