CF284A.Cows and Primitive Roots

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题目描述

The cows have just learned what a primitive root is! Given a prime $p$ , a primitive root is an integer $x$ (1<=x<p) such that none of integers $x-1,x^{2}-1,...,x^{p-2}-1$ are divisible by $p$ , but $x^{p-1}-1$ is.

Unfortunately, computing primitive roots can be time consuming, so the cows need your help. Given a prime $p$ , help the cows find the number of primitive roots .

输入格式

The input contains a single line containing an integer $p$ (2<=p<2000) . It is guaranteed that $p$ is a prime.

输出格式

Output on a single line the number of primitive roots .

输入输出样例

输入#1
```
3
```
输出#1
```
1
```
输入#2
```
5
```
输出#2
```
2
```

说明/提示

The only primitive root is $2.$

The primitive roots are $2$ and $3.$

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