open System

// prelude
let readStr () = stdin.ReadLine()

let read f () = readStr() |> f
let reads f () = readStr().Split() |> Array.map f

let pair = function
| [|a; b|] -> (a, b)
| _ -> failwith "owatta"

let triple = function
| [|a; b; c|] -> (a, b, c)
| _ -> failwith "owatta"

let quad = function
| [|a; b; c; d|] -> (a, b, c, d)
| _ -> failwith "owatta"

let readPair f g () =
  let (a,b) = readStr().Split() |> pair
  (f a, g b)

let readTriple f g h () =
  let (a,b,c) = readStr().Split() |> triple
  (f a, g b, h c)

let inc n = n + 1
let dec n = n - 1

let inline flip f a b = f b a
let rec fix f = fun x -> (f (fix f)) x

module Option =
  let getOr defaultValue = function
  | Some x -> x
  | None -> defaultValue

module Array =
  let modify (arr: _ []) i f =
    arr.[i] <- f arr.[i]

module Array2D =
  let modify (arr: _ [,]) i j f =
    arr.[i, j] <- f arr.[i, j]

// start
let (A,B,H,M) = reads double () |> quad

let pi2=2.*Math.PI
let argH = (H+M/60.)/12.*pi2
let argM = M/60.*pi2

let diff = argH-argM

sqrt (A*A+B*B-2.*A*B*(Math.Cos diff))
|> printfn "%.16f"