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 little boy that has a toothbrush in his mouth'. Find frequency of the letter 'r'

Ex Output:
1


Ex Input:
Sentence: 'a bowl of granola, dried fruit, and bananas'. Find frequency of the letter 'u'

Ex Output:

1