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

Ex Input:
Sentence: 'a person is riding in a cart pulled by a horse'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'apples, pears, and oranges are piled up for sale'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'the guys are doing tricks on their skateboards'. Find frequency of the letter 'g'

Ex Output:

2