remember previous input value in ruby

I have this sample class below.

class MyClass
  def initialize(options = {})
    @input = options[:input]
  end

  def trigger
    # I want to remember previous input value if this method called.
    input
  end
end

How can I store or remember the previous value that was previously input? For example.

my_class = MyClass.new(input: "first")
my_class.trigger
=> first

If I call:

my_class.input = "second"

I want to remember the previous value input which is "fisrt". How can I achieve this?