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NEERC, Central subregion, Rybinsk, October 2002

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B. Flags

Time limit: 1.0 second
Memory limit: 64 MB
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:
Problem illustration

Input

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

Output

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

Sample

inputoutput
3
4
Problem Source: 2002-2003 ACM Central Region of Russia Quarterfinal Programming Contest, Rybinsk, October 2002
To submit the solution for this problem go to the Problem set: 1225. Flags