a, b = input().split()

sa = a
sb = b

len_a = len(sa)
len_b = len(sb)

if len_a != len_b:
    print(a if len_a > len_b else b)
else:
    for i in range(len_a):
        digit_a = int(sa[i])
        digit_b = int(sb[i])
        if digit_a == digit_b:
            continue
        else:
            if (digit_a == 4 and digit_b == 7):
                print(a)
                break
            elif (digit_a == 7 and digit_b == 4):
                print(b)
                break
            else:
                if digit_a > digit_b:
                    print(a)
                else:
                    print(b)
                break
    else:
        # This case is impossible as per problem constraints (A != B)
        pass