input = {};

-- import input from external file
for line in io.lines("./input.txt") do
  table.insert(input, line)
end

parsed = {};

for key, value in pairs(input) do
  -- strip non-numerical chars from input
  local alphastrip = string.gsub(value, "[%a]", "");

  -- if remaining number is 1 char long, double it and then put it into the table
  if string.len(alphastrip) == 1 then
    local doubled = alphastrip .. alphastrip;
    table.insert(parsed, doubled);

  -- if remaining number is 2 chars long, put it into the table as-is
  elseif string.len(alphastrip) == 2 then
    table.insert(parsed, alphastrip);

  -- otherwise fetch first and last digits, concat them, and insert them into the table that way
  else
    local digitstrip = string.match(alphastrip, "%d", 1) .. string.match(alphastrip, "%d", -1);
    table.insert(parsed, digitstrip);
  end
end

result = 0;

-- add all the values stored in `parsed` together
for key, value in pairs(parsed) do
  result = value + result;
end

print(result);