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.
import math

l1 = int(input())
#l2 = input().split()

#l1 = [int(i) for i in l1]
#l2 = [int(i) for i in l2]


r = 0;
if (l1 % 2 != 0):
  n = l1
  for i in range (2, int(math.sqrt(n))):
	  if (n % i == 0):
		  n = i;
  l1 -= n;
  r += 1;

print(int(r + l1 / 2));
		   	   	     		    		 	  	  	