CF284A Cows and Primitive Roots

The cows have just learned what a primitive root is! Given a prime $ p $ , a primitive root  is an integer $ x $ $ (1

The input contains a single line containing an integer $ p $ $ (2

Output on a single line the number of primitive roots .

The only primitive root  is $ 2. $ The primitive roots  are $ 2 $ and $ 3. $