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.
#encoding:utf-8
import math
class Rookie(object):

    def _input(self):
        l1 = raw_input()
        #l1 = x
        n = long(l1.strip())
        return n

    def _output(self):
        print self.r

    def solve(self):
        n = self._input()
        p = 2
        ans = 0
        maxx = n
        if n % 2 == 0:
            self.r = n/2
        else:
            while p <= n:
                if n % p == 0:
                    ans = 1 + (n - p) / 2
                    break
                p+=1
            self.r = ans
            self._output()
if __name__ == '__main__':
    Rookie().solve()