open System
type Sol() =
    member this.Solve() = 
        
        let A = stdin.ReadLine().Split();
        let B = stdin.ReadLine().Split();
        
        let comp s t =
            if Seq.length s > (Seq.length t) then 1
            elif Seq.length s < (Seq.length t) then -1
            else
                let st = Seq.zip s t |> Seq.toArray
                let res = Seq.tryFindIndex (fun p -> (fst p) <> (snd p) ) st
                if Option.isNone res then 0 else (if fst (st.[Option.get res]) > (snd (st.[Option.get res])) then 1 else -1)
        
        let ans = match (comp A.[1] B.[1]) with
                  | 1 -> A.[0]
                  | -1 -> B.[0]
                  | _ -> "-1"
        
        printfn "%s" ans
let mySol = new Sol()
mySol.Solve()