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.
	import java.io.BufferedReader;
	import java.io.IOException;
	import java.io.InputStreamReader;
	import java.io.PrintWriter;
	import java.util.Arrays;
	import java.util.HashMap;
	import java.util.Map;
	import java.util.PriorityQueue;
	import java.util.Scanner;
	import java.util.TreeMap;
	import java.util.*;
	
	public class CF_428_DIV2_B {
		
	
		public static void main(String[] args) throws IOException {
			BufferedReader input = new BufferedReader (new InputStreamReader(System.in));
			
			long num = Long.parseLong(input.readLine());
			
			
			long count = 0;

			if (num%2 != 0) {
				long numSqrt = (long) Math.sqrt(num);
				boolean primeFound = false;
				for (int i = 2; i <= numSqrt; i++) {
					if (num%i == 0) {
						num -= i;
						primeFound = true;
						count++;
						break;
					}
				}
				
				if (primeFound) {
					count += num/2;
				} else {
					count++;
				}
			} else {
				count += num/2;
			}
			
			System.out.println(count);

			input.close();	
		}
	}
