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 truck with a camper sits parked in some vegetation'. Find frequency of the letter 's'

Ex Output:
3

Ex Input:
Sentence: 'two women smiling for a picture while on the ski slope'. Find frequency of the letter 'u'

Ex Output:
1