What Do I Do If My Classmates Are Joking About Doing A School Shooting

This is not the first time this has happened, there are about 5-6 of my classmates ( really troubled ones) are on the edge of getting kicked from school, they sometimes bring up the idea to do a school shooting becouse it " doesn't even matter anymore " in like the dressing room or smth where teachers don't hear it. Safe to say, I don't feel safe anymore around them, + I know that one could even have a gun at home becouse his grandfather was a professional hunter( we are in hungary, you need many permits to have a gun). I really wanna stay anonymus so I can't just walk in to the principals office and just tell them What should I do? Do I report it to the police? Do I leave it as is becouse surely they won't do that?