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

Ex Input:
Sentence: 'three young children playing with a ball in front of a huge bridge'. Find frequency of the letter 'e'

Ex Output:
5


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: 'several colorful umbrellas opened on a table in front of a brick wall'. Find frequency of the letter 'n'

Ex Output:

4