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 sqrt; from itertools import count, islice
def isPrime(n):
    return n > 1 and all(n%i for i in islice(count(2), int(sqrt(n)-1)))
def primes_method4(n):
    out = list()
    out.append(2)
    for num in range(3, n+1, 2):
        if all(num % i != 0 for i in range(2, int(num**.5 ) + 1)):
            out.append(num)
    return out
def div(n,a):
    
    if n==0:
        return 0
    else:
        if n%2==0:
            return n//2
        else:
            if isPrime(n):
                return 1
            else:    
                for i in a:
                    if n%i==0:
                        break
                return 1+ div(n-i,a)
        
if __name__=="__main__":
    n=int(input())
    arr=primes_method4(100000)
    anws=div(n,arr)
    print(anws)