#include <bits/stdc++.h>
using namespace std;
long long int pov(long long int j, long long int i, long long int n) {
  long long int p = 1;
  while (i--) {
    p = (p * j) % n;
  }
  return p;
}
void solve() {
  long long int i, j, n, count = 0;
  cin >> n;
  for (j = 1; j < n; j++) {
    long long int p = 1;
    long long int a[n - 1];
    i = 0;
    while (i < n - 1) {
      p = (p * j) % n;
      a[i] = p;
      i++;
    }
    for (i = n - 1; i > 0; i--) {
      if (i == n - 1) {
        long long int k = (a[i - 1] - 1);
        if (k % n == 0)
          continue;
        else
          break;
      } else {
        long long int k = (a[i - 1] - 1);
        if (k % n != 0)
          continue;
        else
          break;
      }
    }
    if (i == 0) count++;
  }
  cout << count;
  return;
}
int main() {
  solve();
  return 0;
}
