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

Ex Input:
Sentence: 'a bed with a mattress that has nothing on it'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a truck is parked in front of a store'. Find frequency of the letter 't'

Ex Output:
3


Ex Input:
Sentence: 'a girl wearing a motorcycle helmet and a dog wearing a camo hat'. Find frequency of the letter 'a'

Ex Output:

9