# Computer Transformation

## 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?

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 consecutive zeroes pairs that will appear in the sequence after n steps.

## 样例

样例输入 #1

```
2
3
```

样例输出 #1

```
1
1
```

## 来源

Southeastern Europe 2005