In how many ways can you tile a $3\times n$ rectangle with $2\times 1$ dominoes?
Here is a sample tiling of a $3\times 12$ rectangle.
Input consists of several test cases followed by a line containing -1. Each test case is a line containing an integer $0 \leq n \leq 30$. For each test case, output one integer number giving the number of possible tilings.
|Sample Input 1||Sample Output 1|
2 8 12 -1
3 153 2131