def main():
    Sa, Pa, Xa = map(str, input().split())
    Sb, Pb, Xb = map(str, input().split())

    if Pa == Pb:
        print(-1)
        return
    else:
        if len(Pa) > len(Pb):
            print(Sa)
            return
        elif len(Pa) < len(Pb):
            print(Sb)
            return
        else:
            for i in range(len(Pa)):
                if Pa[i] > Pb[i]:
                    print(Sa)
                    return
                elif Pa[i] < Pb[i]:
                    print(Sb)
                    return
                else:
                    continue


if __name__ == "__main__":
    main()