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.
# Problem: B. Divisor Subtraction
# Contest: Codeforces - Educational Codeforces Round 54 (Rated for Div. 2)
# URL: https://codeforces.com/contest/1076/problem/B
# Memory Limit: 256 MB
# Time Limit: 2000 ms
# 
# Powered by CP Editor (https://cpeditor.org)

def fun(n):
	for _ in range(2,int(pow(n,(1/2)))+1):
		if n%_==0:
			return _
	return n 
		
n=int(input())

print((n-fun(n))//2+1)