A, B = input().split()
N = max(len(A), len(B))
AA = f"{A:0>{N}}"
BB = f"{B:0>{N}}"

for a, b in zip(AA, BB):
    if a == b:
        continue
    a = int(a)
    b = int(b)
    if a == 4 and b == 7 or a == 7 and b == 4:
        a, b = b, a

    if a > b:
        print(A)
        exit()
    elif a < b:
        print(B)
        exit()