There are three towers. The objective of the game is to move all the disks over to tower #3, but you can't place a larger disk onto a smaller disk. To play the game or learn more about the Tower of Hanoi, check the Resources tab.

Create a function that takes a number discs as an argument and returns the minimum amount of steps needed to complete the game.

Examples

tower_hanoi(3) ➞ 7

tower_hanoi(5) ➞ 31

tower_hanoi(0) ➞ 0

Notes

• The amount of discs is always a positive integer.
• 1 disc can be changed per move.