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


val () =
    let
        val x = readInt ()
        val y = readInt ()
        val z = readInt ()

        val diff = Int.abs(x - y)
        
        val ans =
            if z <= diff then (Int.max(x, y) - diff) + z
            else Int.max(x, y) + (z - diff) div 2
    in
        print (Int.toString ans ^ "\n")
    end