a, b = [ i for i in input().split() ]

if len(a) > len(b):
    print(a)
elif len(a) < len(b):
    print(b)
else:
    for i in range(len(a)):
        if a[i] != b[i]:
            if (a[i],b[i]) == ("4","7"):
                print(a)
            elif (a[i],b[i])  == ("7","4"):
                print(b)
            else:
                if ord(a[i]) > ord(b[i]):
                    print(a)
                else:
                    print(b)
            break