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 prime(n):
    i = 1
    cont = 0
    while(i * i <= n):
        if(n % i == 0):
            cont += 1
            if(i * i != n):
                cont += 1
        i += 1
    return cont

n = int(input())
primes = prime(n)
nprimo = 3
sub = 0

if(n % 2 == 0):
    sub = n//2
else:
    if(primes > 2):
        while(n > 0):
            if(n % 2 == 0): break
            if(n % nprimo == 0):
                n = n - nprimo
                sub += 1
            else:
                nprimo += 1
        sub += n//2
    else:
        sub = 1
print(sub)
  	 	    			  	  			  					