-- 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 total = 0
-- print all line numbers and their contents
for _, line in pairs(lines) do
	for a, b in string.gmatch(line, "mul%((%d+),(%d+)%)") do
		---@diagnostic disable-next-line: redefined-local
		local a, b = tonumber(a), tonumber(b)
		total = total + (a * b)
	end
end

io.output():write(total)