using System;

namespace yukicoder
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] s = Console.ReadLine().Split(' ');
            int a = int.Parse(s[0]);//目の前の野菜
            int b = int.Parse(s[1]);//目の前の肉
            int c = int.Parse(s[2]);//1つの野菜を食べるための肉の数
            int d = int.Parse(s[3]);//最大数
            int count = 0;
            int n = b / c;
            int t =d - c;
            int sum=0;
            if (t <= 0||c>b)
            {
                Console.WriteLine(count);
            }
            else
            {
                if (n >= a)
                {
                    count = a;
                }
                else if(d == n)
                {
                    count=n;
                }
                else
                {
                    int u =a - n;
                    a -= u;
                    sum = a + b;
                    for(; ; )
                    {
                        sum -= c;
                        n -= 1;
                        if (sum < d)
                        {
                            count = n;
                            break;
                        }
                    }
                }
                Console.WriteLine(count);
            }

        }
    }
}