In this task, you need to count the number of times the given letter appears in the given sentence.

Ex Input:
Sentence: 'a person trying to flip a skateboard in a garage'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'a black computer with a screen reading "press any key to begin."'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a man driving a motorcycle down a street with a  woman on back of it'. Find frequency of the letter 't'

Ex Output:

5