This is pretty much how most people implement the rule in Czech Republic for mandatory masks in public - anything that covers you mount and nose is fine, including self made cloth masks and even scarves. The government even said they are find with that at multiple ocasions.

So "I don't have a mask" is really no argument, as long as you have at least one piece of clothing on you, you can wrap it around your mount & nose. There, you have a mask.