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.
# -*- coding: utf-8 -*-
"""
Created on Sun Nov 25 19:04:01 2018

@author: hitesh b
"""
import math

n=int(input())
count=0

while(n%2!=0):
    flag= True
    for i in range(3,(int)(math.sqrt(n)+1)):
        if(n%i == 0):
            n-=i
            flag=False
            break
    if(flag):
        n=0
    count+=1

count+= int(n/2)

print(count)