1 s   64 MB

Description

In how many ways can you tile a 2xn rectangle by 2x1 or 2x2 tiles? Here is a sample tiling of a 2x17 rectangle.

Input

Input is a sequence of lines, each line containing an integer number 0 <= n <= 50.

Output

For each line of input, output one integer number in a separate line giving the number of possible tilings of a 2xn Rectangle.

Sample Output

2
8
12
50
3
171
2731
750599937895083

Source

The UofA Local 2000.10.14