Problems

# New-year tree

# New-year tree

For decoration of the New-year tree Peter has in the order a garland from the `N`

lamps and **К** of different paints for their painting. How many methods can he to do it, if he must no 2 identical colors be alongside?

#### Input

The amount of lamps is `N`

, the amount of different paints is **К**. (`1 ≤ K`

, `N ≤ 15`

).

#### Output

Amount of methods of painting. If Peter can not paint a garland after the described requirements, to show out `-1`

.

Input example #1

6 2

Output example #1

2