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

Ex Input:
Sentence: 'the counter of a doctor's office, including a laptop, cotton swabs, and tongue depressors'. Find frequency of the letter 'g'

Ex Output:
2


Ex Input:
Sentence: 'a photo of a toilet which is not clean'. Find frequency of the letter 'w'

Ex Output:
1


Ex Input:
Sentence: 'a man serving himself pizza in a wooden booth'. Find frequency of the letter 'n'

Ex Output:

4