using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
 
class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        int[] inpt = Reader.GetInt();
        int total = inpt[0];
        int maxItemCount = inpt[1];
        
        this.CreatePrimeNumberList(total);
        int ans = 1;
        if(total % 2 == 0) {
            ans = total / 2;
        } else
        {
            foreach (int num in PrimeNumberList)
            {
                if(total % num == 0) {
                    int tmp = total / num;
                    ans = tmp * (num / 2);
                    break;
                }
            }
            
        }
        Console.WriteLine(ans);
    }
    
    private List<int> PrimeNumberList = new List<int>();
    
    private void CreatePrimeNumberList(int max) {
        bool[] flags = new bool[max+1];
        List<int> list = new List<int>();
        
        for(int i=2; i<max; i++) {
            if(!flags[i]) {
                list.Add(i);
                for(int j=1; j<=max/i; j++) {
                    flags[i*j] = true;
                }
            }
        }
        this.PrimeNumberList = list;
    }

    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"


21 2


 
";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
        public static int[] GetInt(char delimiter = ' ', bool trim = false)
        {
            string inptStr = ReadLine();
            if (trim)
            {
                inptStr = inptStr.Trim();
            }
            string[] inpt = inptStr.Split(delimiter);
            int[] ret = new int[inpt.Length];
            for (int i = 0; i < inpt.Length; i++)
            {
                ret[i] = int.Parse(inpt[i]);
            }
            return ret;
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}