import sys
sys.set_int_max_str_digits(0)

A, B = input().split()

if len(A) > len(B):
    print(A)
elif len(A) < len(B):
    print(B)
else:
    N = len(A)
    for i in range(N):
        a, b = A[i], B[i]
        if a == b:
            continue
        if a == '4' and b == '7':
            exit(print(A))
        elif a == '7' and b == '4':
            exit(print(B))
        else:
            if int(a) > int(b):
                exit(print(A))
            else:
                exit(print(B))