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


fun findAns a b c =
    if a = b andalso b = c then a
    else if a <> b andalso b <> c andalso c <> a then List.hd (List.filter (fn x => x <> a andalso x <> b andalso x <> c) [0, 1, 2, 3])
    else if a = b then c
    else if b = c then a
    else b


val () =
    let
        val a = readInt ()
        val b = readInt ()
        val c = readInt ()
                                 
        val ans = findAns a b c
    in
        print (Int.toString ans ^ "\n")
    end