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

#### Input

The amount of lamps is **n**, the amount of different paints is **k** (**1** ≤ **k**, **n** ≤ **15**).

#### Output

Print the number of painting ways. If Peter can not paint a garland after the described requirements, to show out **-1**.

Input example #1

6 2

Output example #1

2