static private double avg(double a, double b, double c, double d)
public static void Main()
Console.WriteLine("1st number:");
double first = double.Parse(Console.ReadLine());
Console.WriteLine("2nd number:");
double second = double.Parse(Console.ReadLine());
Console.WriteLine("3rd number:");
double third = double.Parse(Console.ReadLine());
Console.WriteLine("4th number:");
double fourth = double.Parse(Console.ReadLine());
Console.WriteLine("Average: " + avg(first, second, third, fourth));