def main():
    A, B = input().split()

    if len(A) > len(B):
        print(A)
        return

    if len(B) > len(A):
        print(B)
        return

    for a_elm, b_elm in zip(A, B):
        match a_elm:
            case "4":
                match b_elm:
                    case "7":
                        print(A)
                        return
                    case "4":
                        continue
                    case num:
                        if 4 > int(num):
                            print(A)
                        else:
                            print(B)
                        return
            case "7":
                match b_elm:
                    case "4":
                        print(B)
                        return
                    case "7":
                        continue
                    case num:
                        if 7 > int(num):
                            print(A)
                        else:
                            print(B)
                        return
            case num:
                if int(num) < int(b_elm):
                    print(B)
                    return
                if int(num) > int(b_elm):
                    print(A)
                    return


if __name__ == "__main__":
    main()