You are given an integer number n. The following algorithm is applied to it:

  1. if n = 0, then end algorithm; 
  2. find the smallest prime divisor d of n; 
  3. subtract d from n and go to step 1. 



Determine the number of subtrations the algorithm will make.

Input

The only line contains a single integer n (2 ≤ n ≤ 10^{10}).

Output

Print a single integer — the number of subtractions the algorithm will make.

Examples

Input


5


Output


1


Input


4


Output


2

Note

In the first example 5 is the smallest prime divisor, thus it gets subtracted right away to make a 0.

In the second example 2 is the smallest prime divisor at both steps.
#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
long long int trial(long long int n) {
  for (long long int d = 3; d * d <= n; d += 2) {
    if (n == 1) break;
    while (!(n % d)) {
      return d;
    }
  }
  return n;
}
int main() {
  long long int n;
  cin >> n;
  if (!(n % 2))
    cout << n / 2 << "\n";
  else {
    n -= trial(n);
    cout << (n / 2) + 1 << "\n";
  }
  return 0;
}
