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

Ex Input:
Sentence: 'a black bear sitting in the grass taking a rest'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'a group of people seated in chairs together and facing the same direction, with one man holding a soccer ball in his hands'. Find frequency of the letter 'm'

Ex Output:
2


Ex Input:
Sentence: 'a cat sits in a kitchen sink as it examines the faucet'. Find frequency of the letter 'a'

Ex Output:

6