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 pf(n):
	if n%2 == 0:
		return 2

	i = 3
	while i*i<=n:
		if n%i == 0:
			return i
		else:
			i += 2
	return n

n = int(input())
if not n&1:
	print(n//2)
else:
	ans=0
	x = pf(n)
	while n%2!= 0:
		n -= x
		if n <= 0:
			break
		ans += 1
	print(ans + n//2)

