Odd-Even elimination

The integers 1 through 12345 (inclusive) are written in a row in ascending order. You and your friend take turns removing numbers according to the following rules:

  • Step 1: You remove numbers from all odd positions (i.e. 1, 3, 5, ..., 12345).
  • Step 2: Your friend removes numbers from all even positions (i.e. 4, 8, ... because 2 is now in position #1 and 6 is in position #3, and so on).
  • Step 3: If there is more than one number remaining on the list, repeat the steps above.

What is the last number remaining after completing these steps?

The diagram to the right illustrates the case for a list of numbers 1 to 8.


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