#include <bits/stdc++.h>
using namespace std;
int mod(int a, int b, int c) {
  if (b == 0) return 1;
  if (b == 1) return a % c;
  if (b & 1)
    return (a * mod(a, b - 1, c)) % c;
  else {
    int tmp = mod(a, b >> 1, c);
    return (tmp * tmp) % c;
  }
}
bool chk(int x, int p) {
  if (mod(x, p - 1, p) != 1) return false;
  for (int i = 1; i <= p - 2; i++) {
    int tmp = mod(x, i, p);
    if (tmp == 1) return false;
  }
  return true;
}
int main() {
  int n;
  while (scanf("%d", &n) != EOF) {
    int ans = 0;
    for (int i = 1; i < n; i++)
      if (chk(i, n)) ans++;
    printf("%d\n", ans);
  }
  return 0;
}
