#include <bits/stdc++.h>
using namespace std;
long long binpow(long long a, long long b, long long m) {
  a %= m;
  long long res = 1;
  while (b > 0) {
    if (b & 1) res = res * a % m;
    a = a * a % m;
    b >>= 1;
  }
  return res;
}
int main() {
  ios::sync_with_stdio(false);
  long long p, count, finalcount = 0;
  cin >> p;
  for (int i = 1; i < p; ++i) {
    count = 0;
    for (int j = 1; j < p - 1; ++j) {
      if ((binpow(i, j, p) - 1 + p) % p != 0) {
        count++;
      }
    }
    if ((binpow(i, p - 1, p) - 1 + p) % p == 0) {
      count++;
    }
    if (count == p - 1) {
      finalcount++;
    }
  }
  cout << finalcount << endl;
  return 0;
}
