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