I just started to learn ruby and I have a small project I'm working on. I'm making a simple **two** number calculator. What I want to do is get the user to input two numbers and then ask them if they would like to add/subtract/multiply them. My problem is, I want a message to fire if the user doesn't type in add/subtract/multiply. Say the user types **Ad** instead of **Add**, I want the computer to say "I don't understand!" I'm not sure how to execute this.

Here is my code so far.

```
puts "Welcome to math.rb!"
puts "Enter a number!"
     user = gets.to_i
puts "Enter another number!"
    user2 = gets.to_i
puts "What would you like to do with your number? You can add, subtract, or multiply!"

math = gets.chomp.downcase 
if math == "add"
    puts user + user2
end 
if math == "subtract"
    puts user - user2
end
if math == "multiply"
    puts user * user2
end
if math != ["add", "subtract", "multiply"]
    puts "I don't understand"
end

```