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 = input()

isprime = [1 for i in range(int(n**0.5)+2)]
isprime[0] = isprime[1] = 0

def sieve():
    global isprime

    n = len(isprime)

    touched = [0 for i in range(n)]

    for i in range(2, int(n**0.5)+2):

        if not touched[i]:
            touched[i] = 1
            isprime[i] = 1

        for j in range(2*i, n, i):

            if not touched[j]:
                touched[j] = 1
                isprime[j] = 0


sieve()


def SPF(n):

    for i in range(2, int(n**0.5)+2):
        if n%i == 0 and isprime[i]:
            return i

    return n


    
print n/SPF(n)
