fun readInt () =
    valOf (TextIO.scanStream (Int.scan StringCvt.DEC) TextIO.stdIn)


val () =
    let
        val a = readInt ()
        val b = readInt ()
        val c = readInt ()
        val d = readInt ()
        
        fun findAns 0 _ _ = 0
          | findAns _ 0 _ = 0
          | findAns v m s =
            if m < c then 0
            else if d < v + c + s then 0
            else 1 + findAns (v - 1) (m - c) (1 + c + s)

        val ans = findAns a b 0
    in
        print (Int.toString ans ^ "\n")
    end