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

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


val () =
    let
        val sa = readStr ()
        val pa = readLargeInt ()
        val _ = readStr ()

        val sb = readStr ()
        val pb = readLargeInt ()
        val _ = readStr ()

        val ans =
            if pa = pb then "-1"
            else if pa < pb then sb
            else sa
    in
        print (ans ^ "\n")
    end