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

Ex Input:
Sentence: 'a man is taking a picture of a man and woman'. Find frequency of the letter 'a'

Ex Output:
8


Ex Input:
Sentence: 'a person on a surfboard in the surf of a wave'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'fire hydrant has two stickers on it to give it a "face"'. Find frequency of the letter 'f'

Ex Output:

2