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 get_smallest_prime(x):
    if x%2==0:
        return 2
    i = 3;  
    while(i * i <= x): 
        if (x % i == 0): 
            return i 
        i += 2 
  
    return x 

n=int(raw_input())

if n%2==0:
    print(n/2)
else:
    count=0
    x=get_smallest_prime(n)
    count=1+(n-x)/2
    print(count)
    