Count the number of max consecutive "a"'s from a string. Python 3

Count the number of max consecutive "a"'s from a string. Python 3

Say that the user inputs:
"daslakndlaaaaajnjndibniaaafijdnfijdnsijfnsdinifaaaaaaaaaaafnnasm"
How would you go about finding the highest number of consecutive "a" and
how would you remove the "a"'s and leave only 2 of them instead of the
large number of them before.
I was thinking of appending each letter into a new empty list but i'm not
sure if that's correct or what to do after.
I really don't know where to begin with this one but this is what i'm
thinking:
Ask the user for input.
Create an empty list
Append each letter from the input into the list
What's next I have no idea.
second edit (something along these lines):
sentence = input("Enter your text: ")
new_sentance = " ".join(sentence.split())
length = len(new_sentance)
alist = []
while (length>0):
alist
print ()