let split str delim =
  let rec doit s acc =
    match
      try Some (String.index s delim)
      with _ -> None
    with
    | None -> s :: acc
    | Some i ->
        let s1 = String.sub s 0 i in
        let s2 = String.sub s (i + 1) (String.length s - String.length s1 - 1) in
        doit s2 (s1 :: acc)
  in
  List.rev (doit str [])

let distance (x1, y1) (x2, y2) =
  sqrt ((x1 -. x2)*.(x1 -. x2) +. (y1 -. y2)*.(y1 -. y2))

let () =
  let l = read_line () in
  match List.map float_of_string (split l ' ') with
  | [] | [_] | _::_::[] | _::_::_::[] -> exit 1
  | x1 :: y1 :: x2 :: y2 :: _ -> Printf.printf "%f\n" (distance (x1, y1) (x2, y2))