using System;
using System.Linq;

namespace lv1_804
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] input = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            int a = input[0], b = input[1], c = input[2], d = input[3];
            
            while (a + c * a >= d)
            {
                if (a == 0) break;
                a--;                                
            }
            Console.WriteLine(a);
        }
    }
}