描述

A sequence consisting of one digit, the number 1 is initially written into a computer. At each successive time step, the computer simultaneously tranforms each digit 0 into the sequence 1 0 and each digit 1 into the sequence 0 1. So, after the first time step, the sequence 0 1 is obtained; after the second, the sequence 1 0 0 1, after the third, the sequence 0 1 1 0 1 0 0 1 and so on.

How many pairs of consequitive zeroes will appear in the sequence after n steps?

输入

Every input line contains one natural number n (0 < n <= 1000).
 

输出

For each input n print the number of consequitive zeroes pairs that will appear in the sequence after n steps.

OpenJudge - 9290:Pku2680 Computer Transformation

翻译

描述

最初由一个数字1组成的序列被写入计算机。在每一个连续的时间步长中，计算机同时将每个数字0转换成序列1，并将每个数字1转换成序列0 1。因此，在第一次时间步后，得到序列0 1;在第二个之后，就是序列1 0 0 1，在第三个之后，就是序列0 1 1 0 1 0 0 1，以此类推。

n步之后，序列中会出现多少对连续的0 ?

输入

输入的每一行包含一个自然数n (0 < n <= 1000).

输出

对于每一个输入的n，输出经过n步后出现的相邻0的数量。