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
n = int(input())
flag = 0
def sieveofEr(n):
	i = 2
	primeno = [False]*n
	l = []
	while i<=n:	
		j = i*i
		while j <=n:
			primeno[j-1] = True
			j = j + i
		i = i + 1
	for i in range(1,len(primeno)):
		if primeno[i] == False:
			l.append(i+1)
	return l

t = int(sqrt(n))
p = sieveofEr(t)
for i in range(len(p)):
	if n%p[i] == 0:
		flag = 1
		break
if flag == 0:
	print(1)
else:
	if p[i]%2 == 1:
		print((n-p[i])//2+1)
	else:
		print(n//2)