#include <bits/stdc++.h>
using namespace std;
int prime;
long long ans;
int flag = 1;
long long mypow(long long x, long long p, long long mod) {
  long long ret = 1;
  x %= mod;
  while (p > 0) {
    if (p & 1) ret = (ret * x) % mod;
    p = p >> 1;
    x = (x * x) % mod;
  }
  return ret;
}
int main() {
  cin >> prime;
  for (int i = 1; i < prime; i++) {
    for (int j = 1; j < prime - 1; j++)
      if (mypow((long long)i, (long long)j, (long long)prime) - 1 == 0) {
        flag = 0;
        break;
      }
    if (flag) ans++;
    flag = 1;
  }
  printf("%I64d\n", ans);
  return 0;
}
