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


val () =
    let
        val al = readInt ()
        val bl = readInt ()
        val a_s = readInt ()
        val b_s = readInt ()

        fun findAns x =
            if x mod al = a_s andalso x mod bl = b_s then x
            else findAns (x + 1)

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