1 s   64 MB

## Description

In how many ways can you tile a 3xn rectangle with 2x1 dominoes? Here is a sample tiling of a 3x12 rectangle.

## Input

Input consists of several test cases followed by a line containing -1. Each test case is a line containing an integer 0 <= n <= 30.

## Output

For each test case, output one integer number giving the number of possible tilings.

### Sample Output

2
8
12
-1
3
153
2131

## Source

Waterloo local 2005.09.24