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 min_prime(x):
    i = 2
    mmin = 0
    while i <= x:
        if x % i == 0:
            mmin = i
            break
        i += 1
    return mmin

import sys
n = int(input())
ctr = 0
check = min_prime(n)
#print(check)
if check == n:
    print(1)
    sys.exit()
if n % 2 == 0:
    ctr = n/2
else:
    ctr = (n-1)/2
ctr  = int(ctr)
print(ctr)
   
