Hashmap design problem

I need to create a custom class/data structure, probably a hashmap..

Normally one puts to a hashmap like so:
myMap.put(myKey, myThing);

This doesn't quite suite my needs, What I need is to remember the most recent *2* things for any key.
So that if I do:
myMap.put(a, 1);
myMap.put(a, 2);
I can get back either the 1 or the 2.
Furthermore, if I do:
myMap.put(a, 3);
then the 1 would disappear and I'd have available the 2 or the 3.

I'd suggestions on how to implement this, whether with hashmap or if you have a better idea, i'm listening.

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