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

Ex Input:
Sentence: 'there is a woman pointing at something with her dog'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'a couple of people that are on a baseball field'. Find frequency of the letter 'c'

Ex Output:
1


Ex Input:
Sentence: 'a guy on top of a wave on his surf board'. Find frequency of the letter 'n'

Ex Output:

2