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

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: 'a cat sleeping near lots of pairs of shoes'. Find frequency of the letter 'r'

Ex Output:
2


Ex Input:
Sentence: 'a man rides a surfboard on a large wave'. Find frequency of the letter 'a'

Ex Output:

7