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 eratosthenes(n):                      # n - число, до которого хотим найти простые числа
    sieve = list(range(n + 1))
    #print(sieve)
    sieve[1] = 0                          # без этой строки итоговый список будет содержать единицу
    prime = []
    for i in sieve:
        if i > 0:
            prime.append(i)
            for j in range(i * i, len(sieve), i):
                sieve[j] = 0
    #return sieve
    return prime


n = int(input())
s = 0
p = eratosthenes(100000)


if n % 2 == 0:
    print(n // 2)
else:
    for i in p:
        if n % i == 0:
            print(1 + (n - i) // 2)
            break
    print(1)
