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

Ex Input:
Sentence: 'a man using a video game controller in a room'. Find frequency of the letter 'n'

Ex Output:
4


Ex Input:
Sentence: 'a little dog on a table while a dog groomer cuts its fur'. Find frequency of the letter 'r'

Ex Output:
3


Ex Input:
Sentence: 'some slices of pizza with some green toppings'. Find frequency of the letter 's'

Ex Output:

5