let ``No.18 うーさー暗号`` () =
    let f n (c:char) = string <| (char)((int c + (n % 26)) % 65 % 26 + 65)
    stdin.ReadLine()
    |> Seq.rev
    |> Seq.mapi f
    |> Seq.rev
    |> Seq.reduce (+)
    |> printfn "%s"
``No.18 うーさー暗号`` ()