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

Ex Input:
Sentence: 'a parking meter painted green with a sign that describes it as not a parking meter'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'a young boy standing in front of a counter with dougnuts'. Find frequency of the letter 'o'

Ex Output:
6


Ex Input:
Sentence: 'a person doing a trick on a snowboard over a hill'. Find frequency of the letter 'r'

Ex Output:

4