A, B = input().split()

def compare_custom(a_str, b_str):
    # Check if the lengths differ
    len_a, len_b = len(a_str), len(b_str)
    if len_a != len_b:
        return a_str if len_a > len_b else b_str
    
    # Compare each digit from left to right
    for a_digit, b_digit in zip(a_str, b_str):
        if a_digit == b_digit:
            continue
        # Handle 4 and 7 cases
        if (a_digit == '4' and b_digit == '7'):
            return a_str
        elif (a_digit == '7' and b_digit == '4'):
            return b_str
        else:
            # Standard comparison for other digits
            return a_str if a_digit > b_digit else b_str
    
    # The two numbers are equal (impossible as per problem constraints)
    return a_str

result = compare_custom(A, B)
print(result)