import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
long n = scanner.nextLong();
long ans = 0;
if (n % 2 == 0) ans = n / 2;
else {
long t = n;
for (long i = 2; i * i <= n; i++) {
if (n % i == 0) {
t = i;
break;
}
}
ans++;
n -= t;
ans += n >> 1;
}
System.out.println(ans);
}
}