public static void rec(int n, int z, int sum, int y)
public static void Main(string[] args)
Console.Write("Natural number: "); int n = int.Parse(Console.ReadLine());
Console.WriteLine("===================");
if (n < 1) Console.WriteLine("The number you have written is not a natural number!");
int z = 0; int sum = 1; int y = 1;
Console.WriteLine("===================");