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 isPrime(n):
    i = 2
    
    while(i * i <= n):
        if(n % i == 0):
            return False
            
        i += 1
            
    return True
    

n = int(input())
subtractions = 0

if(n % 2 == 0):
    subtractions = n // 2

elif(isPrime(n)):
    subtractions = 1

else:
    # Find smallest prime factor of n
    i = 2
    
    while(i * i <= n):
        if(n % i == 0 and isPrime(i)):
            d = i
            break
        
        i += 1
    
    # Subtract d from n
    n -= d
    
    # Count of subtractions
    subtractions = n // 2 + 1
    
print(subtractions)