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 math import *

def cin(): # To take limited number of inputs
    return map(int,input().split())

def cins(): # To take space sepreated strings
    return input.split()

def cino(test=False): # To take individual int input (test = False)
    if not test:
        return int(input())
    else: # To take string input (test = True)
        return input()

def cina(): # array input
  return list(map(int,input().split()))

def ssplit(): # multiple string input
    return list(input().split())

def printlist(l): # To print space seperated array
    for i in l:
        print(i,end=" ")

def smallestDivisor(n): 
    if (n % 2 == 0): 
        return 2; 
    i = 3;  
    while(i * i <= n): 
        if (n % i == 0): 
            return i; 
        i += 2; 
    return n


def main():
    n = cino()
    cnt = 0
    print(1 + (n-smallestDivisor(n))//2)

if __name__ == '__main__':
    main()