a = io.read():reverse()
b = io.read():reverse()
if #a < #b then
  a = a .. string.rep("0", #b - #a)
elseif #b < #a then
  b = b .. string.rep("0", #a - #b)
end
mul = 1
ans = 0
for i = 1, #a do
  if a:byte(i) ~= b:byte(i) then ans = ans + mul end
  mul = mul * 2
end
print(ans)