-- see if the file exists
local function file_exists(file)
	local f = io.open(file, "rb")
	if f then
		f:close()
	end
	return f ~= nil
end

-- get all lines from a file, returns an empty
-- list/table if the file does not exist
local function lines_from(file)
	if not file_exists(file) then
		return {}
	end
	local lines = {}
	for line in io.lines(file) do
		lines[#lines + 1] = line
	end
	return lines
end

-- tests the functions above
local file = "input"
local lines = lines_from(file)

local input = ""
for _, line in pairs(lines) do
	input = input .. line
end

local instructions = {}
-- print all line numbers and their contents
for pos, a, b in string.gmatch(input, "()mul%((%d+),(%d+)%)") do
	---@diagnostic disable-next-line: redefined-local
	local a, b = tonumber(a), tonumber(b)
	local product = a * b

	instructions[#instructions + 1] = {
		pos = pos,
		product = product,
	}
end

for pos in string.gmatch(input, "()do%(%)") do
	instructions[#instructions + 1] = { pos = pos, enable = true }
end

for pos in string.gmatch(input, "()don't%(%)") do
	instructions[#instructions + 1] = { pos = pos, enable = false }
end

table.sort(instructions, function(a, b)
	return a.pos < b.pos
end)

local total = 0
local enabled = true
for _, instruction in ipairs(instructions) do
	if instruction.enable ~= nil then
		enabled = instruction.enable
	elseif enabled then
		total = total + instruction.product
	end
end

io.output():write(total)