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 is_prime(n):
    for i in range(2,int(n**0.5)+1):
        if n%i==0:
            return False
    return True


n=int(raw_input())

if n%2==0:
    print(n/2)
elif is_prime(n):
    print(1)
else:
    x=1
    while x<=10:
        temp=n**(1.0/x)
        if is_prime(temp):
            print(n/(temp))
            break
        x+=1