How to Limit the Number of enemies that Spawn?

As of now, it is set so that

System -> Every x seconds -> spawn enemy

After playing for a while, it gets very hard and even unfair with the amount of enemies on screen.

Is there a way to ensure that (for example) when there are 10 enemies, Spawning them stops? And then it continues when there are less than 10?

Thank you very much.

Enemy.Count <= 10 |

Every x seconds | spawn enemy

That seemed to do the trick, thank you !