using System;

namespace No_740
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] a = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
            int N,M,P,Q;
            N = a[0];
            M = a[1];
            P = a[2];
            Q = a[3];

            int count = 0;
            while (N > 0)
            {
                while (P <= Q)
                {
                    N -= 2 * M;
                    P++;
                    count++;
                }
                N -= M;
                count++;
            }

            Console.WriteLine(count);
        }
    }
}