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

Ex Input:
Sentence: 'a red building with a crowd of people outside it near the water'. Find frequency of the letter 'e'

Ex Output:
7


Ex Input:
Sentence: 'a man holding a frisbee high into the air'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a man that is laying down on a surfboard in the water'. Find frequency of the letter 's'

Ex Output:

2