using System;

public class Program

{

    public static void Main()

    {

        var red=0;

        var blue=0;

        var green=0;

        var yellow="";

        if(red<1)

        {

            yellow = "Not used";

        }

        else if(red >=1)

        {

            if(blue>=1)

            {

                yellow = green.ToString();

            }

            else

            {

                yellow = "Not used";

            }

        }

        else

        {

            yellow = "Not used";

        }

        Console.WriteLine("Output: {0}",yellow);

    }

}

​

/**

​

=IF(red < 1,

    "Not used",

    IF(red >= 1,

        IF(blue >= 1,

            green,

            "Not used"),

        "Not used")

)

​

*/