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.
from collections import Counter
import math

def printArr(arr):
    for i in arr:
        print(i,end=" ")
        
def proA(n):
    if(n%2==0):
        return n//2
    i=2
    k=0
    while(True):
        
        if(i*i>n):
            break
        if(n%(i)==0):
            k=i
            break
        i+=1
    if(k==0):
        return 1
    return 1 + (n-k)//2
n=int(input())
print(proA(n))