#include <bits/stdc++.h>
using namespace std;
int INP, AM, REACHEOF;
char BUF[(1 << 12) + 1], *inp = BUF;
const long double PI = acos((long double)-1.0);
bool check(int x, int p) {
  int cur = 1;
  for (int i = (1), _b = (p - 2); i <= _b; i++) {
    cur = (cur * x) % p;
    if (cur == 1) return false;
  }
  cur = (cur * x) % p;
  return cur == 1;
}
int main() {
  int p;
  while (cin >> p) {
    int res = 0;
    for (int x = 0, _a = (p); x < _a; x++)
      if (check(x, p)) ++res;
    cout << res << endl;
  }
  return 0;
}
