Avoid posts with repeated letters on words

[unfv]

Hi, we have used the minimum number of letters per post option to avoid short responses like

"yes"
"you are right!"
"no"


But our users are now posting

"yeeeeeeeeeeeeesssssssss"
"you are right!!!!!!!!!!!!!!!!!!!!!"
"noooooooooooo"


Is there any way to prevent this?

Thanks