The Snake — Area Filling

This challenge is based on the classic videogame "Snake".

Assume the game screen is an n * n square, and the snake starts the game with length 1 (i.e. just the head) positioned on the top left corner.

For example, if n = 7 the game looks something like this:

In this version of the game, the length of the snake doubles each time it eats food (e.g. if the length is 4, after eating it becomes 8).

Create a function that takes the side n of the game screen and returns the number of times the snake can eat before it runs out of space in the game screen.

Examples

snakefill(3) ➞ 3

snakefill(6) ➞ 5

snakefill(24) ➞ 9

Notes

The given number will always be a positive integer (there are no exceptions to handle).