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


val () =
    let
        val a = readInt ()
        val b = readInt ()
        val x = readInt ()
        val y = readInt ()

        val unit = Real.min (Real.fromInt x / Real.fromInt a, Real.fromInt y / Real.fromInt b)
        val ans = (Real.fromInt a) * unit + (Real.fromInt b) * unit
    in
        print ((Real.fmt (StringCvt.FIX (SOME 6)) ans) ^ "\n")
    end