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

n=int(input())
if n%2==0:
  print(n//2)
else:
  if d(n)==n:
    print(1)
  else:
    r=n-d(n)
    print(int(r/2)+1)
   
 