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

Ex Input:
Sentence: 'two boys are doing skateboard jumps in the street'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'group of snowboarders on a snowy trail overlooking a mountain'. Find frequency of the letter 'r'

Ex Output:
5


Ex Input:
Sentence: 'a reflection from a mirrored window of two dogs being walked on a leash'. Find frequency of the letter 'l'

Ex Output:

3