A, B = input().split()

if len(A) > len(B):
    print(A)
    exit()
elif len(B) > len(A):
    print(B)
    exit()

for n in range(len(A)):
    if A[n] == "7" and B[n] == "4":
        print(B)
        exit()
    elif A[n] == "4" and B[n] == "7":
        print(A)
        exit()
    elif int(A[n]) > int(B[n]):
        print(A)
        exit()
    elif int(B[n]) > int(A[n]):
        print(B)
        exit()