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()

primes = {}
aux = [True] * 1000001
start = 2

while (start <= 1000000):
    if (aux[start]):
        primes[start] = True
        for i in range(start * start, 1000001, start):
            aux[i] = False
    start += 1


def getMinimumPrimeDivisor(number):
    for prime in primes:
        if (number % prime == 0):
            return prime


def getResult(n):
    minimumDivisor = getMinimumPrimeDivisor(n)

    if (n in primes or not minimumDivisor):
        return 1
    else:
        return n / 2 if minimumDivisor == 2 else (n - minimumDivisor) / 2 + 1


print(getResult(n))
