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

Ex Input:
Sentence: 'a teenager witting on a futon couch holding gaming controls in both hands'. Find frequency of the letter 'c'

Ex Output:
3


Ex Input:
Sentence: 'a boy that is sitting at a table with pizza'. Find frequency of the letter 's'

Ex Output:
2


Ex Input:
Sentence: 'a picture of two computers on a table'. Find frequency of the letter 'r'

Ex Output:

2