#include <bits/stdc++.h>
using namespace std;
void err(istream_iterator<string> it) { cerr << endl; }
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << a;
  err(++it, args...);
}
const int MAXN = 1e5 + 100;
const int oo = 1e9 + 100;
const int MOD = 1e9 + 7;
const long double EPS = 1e-9;
int main() {
  for (long long n, tc = 1; scanf("%lld", &n) == 1; ++tc) {
    ;
    long long p = -1;
    for (long long i = 2; i * i <= n; ++i) {
      if (n % i == 0) {
        p = i;
        break;
      }
    };
    long long ans = 0;
    if (n & 1) {
      if (p == -1) p = n;
      ans++;
      n -= p;
    }
    ans += n / 2;
    printf("%lld\n", ans);
  }
  return 0;
}
