A, B = map(str, input().rstrip().split())
if len(A) > len(B):
    print(A)
    exit()
elif len(B) > len(A):
    print(B)
    exit()
else:
    for i in range(len(A)):
        if A[i] == '4' and B[i] == '7':
            print(A)
            exit()
        elif A[i]== '7' and B[i] == '4':
            print(B)
            exit()
        elif A[i] > B[i]:
            print(A)
            exit()
        elif B[i] > A[i]:
            print(B)
            exit()
print(A)