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())
if n%2==0:
    resp = n//2
else:
    primos = []
    numeros= [False, False] + [True]*99999
    raiz = 100001**0.5+2;
    for i in range(2, 100001):
        if numeros[i]:
            if i<=raiz:
                for j in range(i*i, 100001, i):
                    numeros[j]=False
            primos.append(i)

    resp = 0
    while n%2!=0:
        if n<=100001 and numeros[n]:
            break
        i = 0
        while i<len(primos) and n%primos[i]!=0:
            i+=1
        if i==len(primos): break
        resp+=1
        n-=primos[i]
    
    if n%2==0:
        resp+=(n//2)
    else:
        resp+=1

print(resp)
		 					    					 					 		  	 	