Flag

Time Limit: 1000 ms Memory Limit: 65536 KiB

Problem Description

On the Day of the Flag of Russia a shop-owner decided to decorate the show-window of his shop with textile stripes of white, blue and red colors. He wants to satisfy the following conditions:

1.   Stripes of the same color cannot be placed next to each other.

2.   A blue stripe must always be placed between a white and a red or between a red and a white one.

Determine the number of the ways to fulfill his wish.

Example. For N = 3 result is following:




Input

N, the number of the stripes, 1 ≤ N ≤ 45.

Output

M, the number of the ways to decorate the shop-window.

Sample Input

3

Sample Output

4

Hint


Source