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 = int(input())


# def gnerateProst(n):
#     res = [2, 3]
#     sqrtN = int(n ** (1 / 2))
#     for k in range(5,sqrtN,2):
#         isProst = True
#         sqrt = int(len(res) ** (1 / 2))
#         for j in range(0,sqrt):
#             if k % res[j] == 0:
#                 isProst = False
#                 break
#         if isProst:
#             res.append(k)
#
#     print(res)
#     return res
#
#
# def getProst(n, prostList):
#     for k in prostList:
#         if n % k == 0:
#             return k
#     return 1


# prostList = gnerateProst(n)
#
#
# res = 0
# while n > 0:
#     p = getProst(n, prostList)
#     n = n - p
#     res += 1
#     print(n)


def getFirstPrime(n):
    sqrt = int(n ** (1/2)) + 1
    for k in range(3,sqrt,2):
        if n % k == 0:
            return k
    return n


if n % 2 == 0:
    print(int(n / 2))
else:
    n = n - getFirstPrime(n)
    print(int(n / 2) + 1)