I am sure you have figured this out, but just in case someone else comes along and wonders the same thing. We round O(2) down to O(1) as a way to express a constant/predictable complexity (the operation is not affected by the size of the input). Even O(123) is still gonna be O(1).

Short read to refresh our memory about it: https://hackernoon.com/big-o-for-beginners-622a64760e2