#include <bits/stdc++.h>
using namespace std;
bool debug = false;
int n, m, k;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
long long ln, lk, lm;
int p;
bool ck(int x) {
  long long tmp = 1;
  for (int j = 1; j < p; j++) {
    if (tmp * (x - 1) % p == 0) {
      if (j == p - 1)
        return 1;
      else
        return 0;
    }
    tmp = (x * tmp + 1) % p;
  }
  return 0;
}
int main() {
  scanf("%d", &p);
  for (int x = 1; x < p; x++) {
    if (ck(x)) m++;
  }
  cout << m << endl;
  return 0;
}
