In how many ways can you tile a 3xn rectangle with 2x1 dominoes? Here is a sample tiling of a 3x12 rectangle.
Input consists of several test cases followed by a line containing -1. Each test case is a line containing an integer 0 <= n <= 30.
For each test case, output one integer number giving the number of possible tilings.
2 8 12 -1
3 153 2131