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

Ex Input:
Sentence: 'three men in military suits are sitting on a bench,'. Find frequency of the letter 'a'

Ex Output:
3


Ex Input:
Sentence: 'a man on a skateboard going down a ramp while people are watching'. Find frequency of the letter 'w'

Ex Output:
3


Ex Input:
Sentence: 'a cat lays down next to a glass with a straw in it'. Find frequency of the letter 'a'

Ex Output:

7