Flags

http://acm.timus.ru/problem.aspx?space=1&num=1225

Time Limit: 1.0 second

Memory Limit: 1 000 KB

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:

1. Input

n – the number of the stripes, 1 <= n <= 45.

2. Output

m – the number of the ways to decorate the shop-window.

3. Sample Input

3

4. Sample Output

4

Problem Source: 2002-2003 ACM Central Region of Russia Quarterfinal Programming Contest, Rybinsk, October 2002

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