OnlineJudge 3 现已推出。点此体验新版：Flag | SDUT OnlineJudge

### 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