A, B = gets.split
L = [A.length, B.length].max
sa = A.rjust(L, "0")
sb = B.rjust(L, "0")

res = catch(:ok) do
  for i in 0...L do
    na = sa[i].to_i
    nb = sb[i].to_i
    case
    when na == 4 && nb == 7 then throw :ok, A
    when na == 7 && nb == 4 then throw :ok, B
    when na > nb then throw :ok, A
    when na < nb then throw :ok, B
    end
  end
end

puts res