open System
type Sol() =
    member this.Solve() = 
        let [| A;B;X;Y |] = stdin.ReadLine().Split() |> Array.map double
        let needY = X / A * B;
        let needX = Y / B * A;
        let ans = if needY <= Y then (X + needY) else (Y + needX)
        printfn "%f" ans

let mySol = new Sol()
mySol.Solve()