using System;

​

public enum Op

{

    Addition,

    Subtraction,

    Multiplication,

    Division

}

​

public class Program

{

    public static void Main()

    {

        // letter ::= 'a' | 'b' | 'c'...

        // word ::= letter | word letter

​

        // <op> ::= "+" | "-" | "/" | "*" 

        // <number> ::= <op> <number> <number> | 0 | 1 | 2 | 3 ...

        // (- 8 (+ 2 2)) = 4

        var result = BausFormCalculation(Op.Subtraction, 8, BausFormCalculation(Op.Addition, 2, 2));

        Console.WriteLine(result);

    }

    public static int BausFormCalculation(Op op, int n1, int n2) =>

        op switch

        {

            Op.Addition => n1 + n2,

            Op.Subtraction => n1 - n2,

            Op.Multiplication => n1 * n2,

            Op.Division => n1 * n2,

            _ => throw new NotImplementedException()

        };

}