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 = {}, {T:byte(1, -1)}
for i = 1, S:len() do
	S_byte_s[i] = S:byte(i)
	T_byte_s[i] = T:byte(i)
end

for i = 1, S:len() do
	if S_byte_s[i] ~= T_byte_s[i] then
		count = count + 1
	end
end
--]]
print(count)
