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 isPrime(n) :
    if (n <= 1) :
        return False
    if (n <= 3) :
        return True
    if (n % 2 == 0 or n % 3 == 0) :
        return False
    i = 5
    while(i * i <= n) :
        if (n % i == 0 or n % (i + 2) == 0) :
            return False
        i = i + 6
    return True

def f(n):
    l = []
    for i in range(2,n+1):
        if n%i==0:
            return(i)
n = int(input())
if (isPrime(n)):
    print(1)
else:
    s, tp = 0, 0
    while True:
        k = n-tp
        n = n-tp
        if n%2==0:
            s+=(n//2)
            break
        if k==0:
            break
        else:
            tp = f(k)
            s+=1
    print(s)