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

Ex Input:
Sentence: 'a black cat laying down on a bed'. Find frequency of the letter 'y'

Ex Output:
1


Ex Input:
Sentence: 'this is a sign in front of a large cathedral'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a man wearing a trench coat talking on a cellphone on a street'. Find frequency of the letter 'e'

Ex Output:

6