#描述#
This is a small but ancient game. You are supposed to write down the numbers 1, 2, 3, ... , 2n - 1, 2n consecutively in clockwise order on the ground to form a circle, and then, to draw some straight line segments to connect them into number pairs. Every number must be connected to exactly one another. And, no two segments are allowed to intersect.
It's still a simple game, isn't it? But after you've written down the 2n numbers, can you tell me in how many different ways can you connect the numbers into pairs? Life is harder, right?

#格式#
##输入格式##
Each line of the input file will be a single positive number n, except the last line, which is a number -1. You may assume that 1 &lt= n &lt= 100.

##输出格式##
For each n, print in a single line the number of ways to connect the 2n numbers into pairs.

#样例1#
##样例输入1##

2
3
-1

##样例输出1##

2
5

#限制#
1000ms
32768KB

#提示#

#来源#
WY