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 smallestDivisor(n): 
	if (n % 2 == 0): 
		return 2; 

	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:
    x = smallestDivisor(n)
    ans = 1
    n = n -x
    ans = ans + n//2
    print(ans)

