// AtCoder My Practice
// author: Leonardone @ NEETSDKASU

[<EntryPoint>]
let main _ =
    let n = stdin.ReadLine() |> int64
    seq { 0L..n }
    |> Seq.map (fun x -> x * x )
    |> Seq.takeWhile ((>) n)
    |> Seq.last
    |> printfn "%d"
    0