Bee

Problem Description

Imagine a honeycomb — a field of hexagonal cells with side length $N$. In the upper-left cell $A$ there is a bee. In one move it can crawl to the cell down, to the cell down-right, or to the cell up-right (the bee does not crawl up or left). It is required to write a program that finds the number of ways in which the bee can crawl from cell $A$ to the opposite cell $B$.

Input Format

The first line contains a single number $N$ — the size of the hexagonal field $(2 \le N \le 12)$.

Output Format

Output a single integer — the number of ways.

2

11

3

291