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.
n=int(input())
import math
def is_prime(n):
    count=0
    for i in range(2, int(math.sqrt(n)+1)):
        if n%i==0:
            count+=1
    if count==0:
        return True
    else:
        return False
def cf(n):
    if n%2==0:
        print(int(n/2))
    else:
        for i in range(2,int(math.sqrt(n)+1)):
            if n%i==0 and is_prime(i)==True:
                print (int(((n- i)/2)+1))
                break
            elif is_prime(n)==True:
                break
cf(n)