open System open System.Collections.Generic [] module Cin = let read f = stdin.ReadLine() |> f let reada f = stdin.ReadLine().Split() |> Array.map f let readChars() = read string |> Seq.toArray let readInts() = readChars() |> Array.map (fun x -> Convert.ToInt32(x.ToString())) [] module Cout = let writer = new IO.StreamWriter(new IO.BufferedStream(Console.OpenStandardOutput())) let print (s: string) = writer.Write s let println (s: string) = writer.WriteLine s let inline puts (s: ^a) = string s |> println let solve() = let [|px;py|] = reada int let [|qx;qy|] = reada int abs (px - qx) + abs (py - qy) |> fun x -> float x / 2.0 |> puts [] let main _ = try solve() with e -> printfn "%s" (e.ToString()) writer.Close() 0 // return an integer exit code