#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
template <typename T, typename T1>
T amax(T &a, T1 b) {
  if (b > a) a = b;
  return a;
}
template <typename T, typename T1>
T amin(T &a, T1 b) {
  if (b < a) a = b;
  return a;
}
void OJ() {}
const long long N = 2e5 + 5;
long long solve() {
  long long p, cnt = 0;
  cin >> p;
  for (long long i = 1; i < p + 1; ++i) {
    long long f = 1;
    long long x = i;
    for (long long j = 1; j < p - 1; j++) {
      if ((x % p - 1 % p) % p == 0) f = 0;
      x = (x % p * i % p) % p;
    }
    if ((x % p - 1 % p) % p) f = 0;
    if (f) cnt++;
  }
  return cout << cnt, 0;
  ;
  return 0;
}
signed main() {
  OJ();
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  solve(), cout << '\n';
  return 0;
}
