Lagy commands "best way to get diamond medal for discovering physics in minecraft"

So, I just mad realy normal world for commands then, I got snowball then i typ this command in repaeter command block

/execute @e[type=snowball] ~ ~ ~ /summon snowball

And i was idiot to dont know when i throw snow ball it will spamm summoning another balls and the another balls spamm another another another then my game dead

"i discovered physics"

How to fix to prevent the world from losing as the last chance like:

This command willl lead to summon alot of snow balls and the entire world will get lost, Are you sure you want to run this command?.