let calc (p: float) q r : float =
    let m = max r (max p q)

    if 2.0 * m > p + q + r then
        m / (p + q + r)
    else
        (p + q + r - m) / (p + q + r)

let main =
    let input = stdin.ReadLine().Split() |> Array.map float
    let p = input.[0]
    let q = input.[1]
    let r = input.[2]
    printfn "%.14f" (calc p q r)