#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
long double PI = acosl(-1);
const long long inf = 1e15;
const int nmax = 1e6 + 5;
bool iscomposit[nmax];
void siv() {
  iscomposit[1] = true;
  for (int i = 2; i < nmax; i++) {
    if (!iscomposit[i]) {
      for (int j = i + i; j < nmax; j += i) {
        iscomposit[j] = true;
      }
    }
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  siv();
  long long n;
  cin >> n;
  for (long long i = 2; i * i <= n; i++) {
    if (n % i == 0 and iscomposit[i] == false) {
      long long ans = 1;
      n -= i;
      ans += n / 2;
      cout << ans << endl;
      exit(0);
    }
  }
  cout << "1" << endl;
}
