Alexei Kouleshov

Hi, i've made a simple form where people can make ticket reservations for an event. Which is working nicely. I've limited the total amount of entries via a code snippet in the functions.php to 200. But since people can reserve multiple tickets per submission (simple number field), this would ultimately lead to more reserved tickets than are available. How can i close the form after the total ticket amount from all the entries has reached 200?