function rot13 (s)
  local byte_a, byte_A = strbyte('a'), strbyte('A')
  s = gsub(s, "(%a)", function (c)   -- change each letter ...
        c = strbyte(c)
        local offset = (c >= 97) and %byte_a or %byte_A
        c = mod(c+13-offset, 26)
        return strchar(c + offset)
      end)
  return s
end


while 1 do
  local line = read()
  if line == nil then break end
  write(rot13(line), '\n')
end