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


fun findAns n =
    if n mod 2 = 0 then findAns (n + 1)
    else n


val () =
    let
        val n = readLargeInt ()

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