local S, T = io.read("*l", "*l")

local count = 0
---[[ パターン1
for i = 1, S:len() do
	if S:sub(i, i) ~= T:sub(i, i) then
		count = count + 1
	end
end
--]]
--[[ パターン2
local S_byte_s, T_byte_s = {S:byte(1, -1)}, {T:byte(1, -1)}
for i = 1, S:len() do
	if S_byte_s[i] ~= T_byte_s[i] then
		count = count + 1
	end
end
--]]
print(count)
