Given a positive integer N, find the smallest number of steps it will take to
reach 1.

There are two kinds of permitted steps:
- You may decrement N to N - 1.
- If a * b = N, you may decrement N to the larger of a and b.

For example, given 100, you can reach 1 in five steps with the following route:
100 -> 10 -> 9 -> 3 -> 2 -> 1.