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

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: 'a man flying through the air on top of a skateboard'. Find frequency of the letter 'h'

Ex Output:
3


Ex Input:
Sentence: 'a table and chairs fill the room in an apartment'. Find frequency of the letter 't'

Ex Output:

4