-- 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)

-- Solution Starts here

---@diagnostic disable-next-line: redefined-local
local function count_xmas_at_index(lines, line_idx, char_idx)
	local line = lines[line_idx]

	local up_idx = line_idx - 1
	local down_idx = line_idx + 1
	local right_idx = char_idx + 1
	local left_idx = char_idx - 1

	local char_count = {}
	char_count["M"] = 0
	char_count["S"] = 0
	if up_idx >= 1 then
		if right_idx <= #line then
			local key = lines[up_idx]:sub(right_idx, right_idx)
			if char_count[key] ~= nil then
				char_count[key] = char_count[key] + 1
			end
		end

		if left_idx >= 1 then
			local key = lines[up_idx]:sub(left_idx, left_idx)
			if char_count[key] ~= nil then
				char_count[key] = char_count[key] + 1
			end
		end
	end

	if down_idx <= #lines then
		if right_idx <= #line then
			local key = lines[down_idx]:sub(right_idx, right_idx)
			if char_count[key] ~= nil then
				char_count[key] = char_count[key] + 1
			end
		end

		if left_idx >= 1 then
			local key = lines[down_idx]:sub(left_idx, left_idx)
			if char_count[key] ~= nil then
				char_count[key] = char_count[key] + 1
			end
		end
	end

	if char_count["M"] == 2 and char_count["S"] == 2 then
		return true
	end

	return false
end

local xmas_count = 0
-- print all line numbers and their contents
---@diagnostic disable-next-line: unused-local
for line_idx, line in ipairs(lines) do
	for char_idx in line:gmatch("()A") do
		if count_xmas_at_index(lines, line_idx, char_idx) then
			xmas_count = xmas_count + 1
		end
	end
end

io.output():write(xmas_count)