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.
is_prime = [0]*1000100

def primes():
	for i in range(2,1000010):
		if(is_prime[i] == 0):
			is_prime[i] = 1
			for j in range(i*i,1000010,i):
					is_prime[j] = -1

n = int(input())
primes()

if(n%2==0): 
	print(n//2)
else: 
	primo = 0
	for i in range(3,int(n**0.5)+2):
		if(is_prime[i] == 1 and n % i == 0):
			primo = i
			break
		
	if(primo == 0):
		n = 0
	print((n-primo)//2 + 1)