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ZOJ Problem Set - 2547
Tri Tiling

Time Limit: 2 Seconds      Memory Limit: 65536 KB

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 Input

2
8
12
-1

Sample Output

3
153
2131

Source: University of Waterloo Local Contest 2005.09.24
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