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#F2515. Cows and Primitive Roots

    ID: 2521 传统题 2000ms 256MiB 尝试: 0 已通过: 0 难度: 3 上传者: 标签>模拟数学数论编程与模拟基础难度共享题库Codeforces英文题面题目来源题面语言

Cows and Primitive Roots

题目描述

A. Cows and Primitive Roots
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

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,x2-1,...,xp-2-1 are divisible by p, but xp-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 .

Input

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

Output

Output on a single line the number of primitive roots .

Examples
Input
3
Output
1
Input
5
Output
2
Note

The only primitive root is 2.

The primitive roots are 2 and 3.

题目来源：fps-www.educg.net-codeforce-1-2833.xml.zip；FPS 共享题包，题包内第 2157 题。保留原作者与原赛事署名。