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