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

Ex Input:
Sentence: 'a dog is shown sitting on rocks by the beach'. Find frequency of the letter 'a'

Ex Output:
2


Ex Input:
Sentence: 'a notebook and pen are left on a park bench'. Find frequency of the letter 'e'

Ex Output:
5


Ex Input:
Sentence: 'a black dog running across a dry grass field'. Find frequency of the letter 'f'

Ex Output:

1