题目描述

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

输入要求

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

输出要求

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

输入样例

2
8
12
-1

输出样例

3
153
2131

提示

来源