using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace tes
{
	class contest
	{
		static void Main(string[] args)
		{
			 var num = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var dp = new bool[num[0]];
            dp[1] = true;
            int count = 0;
            int plate = num[0];
            plate -= 1;

            if(plate%2 != 0)
            {
                count = plate / num[1];
            }
            else
            {
                count = (plate / num[1]) + (plate-plate/num[1])/num[1];
            }

            
            Console.WriteLine(count);
            
		}

	}
}