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.util.*;
import java.lang.*;
import java.io.*;
public class main 
{
	public static long leastFact(long n) 
    { 
		HashSet<Long> hs=new HashSet<Long>();
        for (long i=3;i<=Math.sqrt(n);i+=2) 
        { 
            while(n%i==0)
            { 
                hs.add(i);
                n/=i; 
            }
        } 
        if(n>2) 
            hs.add(n);
        return Collections.min(hs);
    } 
    public static void main(String[] args) throws IOException 
    {
    	BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    	PrintWriter pw=new PrintWriter(System.out);
    	long N=Long.parseLong(br.readLine());
    	if((N&1)!=0)
    	{
    		N-=leastFact(N);
    		long Ans=1;
    		if(N>0)
    			Ans=N>>1;
        	pw.println(Ans);
    	}
    	else pw.println(N>>1);
        pw.flush();
    }
}