using System;
using System.Linq;

public class Program
{
    public static void Main()
    {
        var lst = Console.ReadLine().Split(' ').
                        Select(s => int.Parse(s)).ToList();

        var a = lst[0]; var b = lst[1]; var c = lst[2]; var d = lst[3];

        for (; ; )
        {
            if ((a > 0) && (b >= c) && (d >= c + 1))
            {
                a--;
                b -= c;
                d -= (c + 1);
            }
            else
                break;
        }

        Console.Write("{0}", (lst[0]-a).ToString());

        return;
    }
}