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 = int(A[i]), int(B[i])
        if a == b:
            continue
        if sorted([a, b]) == [4, 7]:
            if a == 4:
                print(A)
            else:
                print(B)
        else:
            if a > b:
                print(A)
            else:
                print(B)
        exit()