fun readInt () =
    valOf (TextIO.scanStream (Int.scan StringCvt.DEC) TextIO.stdIn)


val () =
    let
        val d = readInt ()
        
        val sequence =
            List.rev
                (List.foldl
                     (fn (n, acc) =>
                         List.revAppend (String.explode (Int.toString n), acc))
                     []
                     (List.tabulate (100, (fn n => n + 1)))
                )

        val ans = List.nth (sequence, d - 1)
    in
        print (Char.toString ans ^ "\n")
    end