#include <bits/stdc++.h>
using namespace std;
const long long N = 2e5 + 10, M = N, INF = 0x3f3f3f3f, mod = 1e9 + 7,
                base = 131;
long long n, t, ans;
long long a[N], s[N];
long long phi(long long n) {
  long long res, a;
  res = a = n;
  for (long long i = 2; i <= a / i; i++) {
    if (a % i) continue;
    res = res / i * (i - 1);
    while (a % i == 0) a /= i;
  }
  if (a > 1) res = res / a * (a - 1);
  return res;
}
signed main() {
  long long p;
  cin >> p;
  cout << phi(p - 1);
  return 0;
}
