#include <bits/stdc++.h>
const long long MOD = 1e9 + 7;
using namespace std;
void solve() {
  long long p;
  cin >> p;
  long long c = 0;
  for (long long i = 1; i <= p; i++) {
    bool cond = true;
    long long x = i % p;
    long long t = 1;
    for (long long j = 1; j < p - 1; j++) {
      t = (t * x) % p;
      if (((t - 1) % p) == 0) {
        cond = false;
        break;
      }
    }
    if (cond) {
      long long z = (t * x) % p;
      if ((z - 1) % p == 0) {
        c++;
      }
    }
  }
  cout << c;
  return;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  long long t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
