fun readLargeInt () =
    valOf (TextIO.scanStream (LargeInt.scan StringCvt.DEC) TextIO.stdIn)


val () =
    let
        val n = readLargeInt ()
       
        val ans = Real.toLargeInt IEEEReal.TO_NEAREST (Math.sqrt (Real.fromLargeInt (n div 3)))
    in
        print (LargeInt.toString ans ^ "\n")
    end