using System;

​

public class Program

{

    public static void Main()

    {

        var result = T(12.3, 4);

        Console.WriteLine(result);

    }

​

    public static double T(double xvalue, int n)

    {

        if (n == 0)

            return 1;

        else if (n == 1)

            return xvalue;

        else

            return 2 * xvalue * T(xvalue, n - 1) - T(xvalue, n - 2);

    }

}