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(raw_input())
primos = [True]*1000001
primos[0] = primos[1] = False
p = []
for i in range(2,1001):
	if primos[i]:
		p.append(i)
		for i in range(i*i,1000001,i):
			primos[i]=False
i = 0
ans = 0
while n > 0:
	if n%p[i] == 0:
		ans += n/p[i]
		n -= p[i]*(n/p[i])
	else:
		i += 1
print ans
  	  	  	      		 	  		 	   	 	