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

Ex Input:
Sentence: 'a woman in a tank top reaches out for a frisbee'. Find frequency of the letter 'a'

Ex Output:
6


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 playing baseball on a television set'. Find frequency of the letter 'l'

Ex Output:

4