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

namespace yukicoderTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] str = Console.ReadLine().Split(' ');
            int vegi = int.Parse(str[0]);
            int meat = int.Parse(str[1]);
            int d = int.Parse(str[2]);
            int total = int.Parse(str[3]);
            int cnt = 0;
            while (true)
            {
                if (total < d + vegi || meat < d)
                {
                    break;
                }
                vegi--;
                meat -= d;
                total = total - d+vegi;
                cnt++;
                
            }
            Console.WriteLine(cnt);
        }
    }
}