A. Cows and Primitive Roots
implementation; math; number theory
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 .
The input contains a single line containing an integer p (2 ≤ p < 2000). It is guaranteed that p is a prime.
Output on a single line the number of primitive roots .
The only primitive root is 2.The primitive roots are 2 and 3.