fun readStr () =
    let
        fun scan reader stream = SOME (StringCvt.splitl (not o Char.isSpace) reader (StringCvt.skipWS reader stream))
    in
        valOf (TextIO.scanStream scan TextIO.stdIn)
    end


fun findAns s =
    let
        fun findAnsAux nil _ = nil
          | findAnsAux (h :: tl) 3 =
            #"," :: h :: findAnsAux tl 1
          | findAnsAux (h :: tl) n =
            h :: findAnsAux tl (n + 1)
    in
        String.implode
            (List.rev (findAnsAux (List.rev (String.explode s)) 0))
    end


val () =
    let
        val n = readStr ()

        val ans = findAns n
    in
        print (ans ^ "\n")  
    end