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

Ex Input:
Sentence: 'a double-decker bus covered in children's illustrations driving next to a van'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a plastic tray that has different foods inside of it'. Find frequency of the letter 't'

Ex Output:
6


Ex Input:
Sentence: 'a large clock tower with a clock on it's face'. Find frequency of the letter 'h'

Ex Output:

1