A, B = input().split()
if len(A) != len(B):
    if len(A) > len(B):
        print(A)
    else:
        print(B)
    exit()

compare = ["47", "74"]
for i in range(len(A)):
    if A[i] + B[i] in compare:
        if A[i] == "4":
            print(A)
            exit()
        else:
            print(B)
            exit()
    else:
        if A[i] == B[i]:
            continue
        if int(A[i]) > int(B[i]):
            print(A)
        else:
            print(B)
        exit()