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 ii():
    return int(input())
def mi():
    return map(int, input().split())
def li():
    return list(mi())
MX = 10 ** 5

n = ii()
if n % 2 == 0:
    ans = n // 2
else:
    c = 3
    ans = 0
    while c <= MX:
        if n % c == 0:
            n -= c
            ans += 1
            break
        c += 1
    if ans:
        ans += n // 2
    else:
        ans = 1
print(ans)