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

namespace yuki415
{
    class Program
    {
        static void Main(string[] args)
        {
            var a = scan;
            int n = a[0];
            int d = a[1];
            if (n % d == 0)
            {
                Console.WriteLine(n / d - 1);
            }
            else
            {
                Console.WriteLine(n-1);
            }
        }

        static int[] scan
        {
            get { return Console.ReadLine().Split().Select(int.Parse).ToArray(); }
        }
    }
}