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

Ex Input:
Sentence: 'a man holding a frisbee high into the air'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a police officer who is riding on a horse'. Find frequency of the letter 'p'

Ex Output:
1


Ex Input:
Sentence: 'a red truck driving past a tall yellow house'. Find frequency of the letter 'a'

Ex Output:

4