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

Ex Input:
Sentence: 'a couple of girls are hanging out at a restaurant'. Find frequency of the letter 'l'

Ex Output:
2


Ex Input:
Sentence: 'a giraffe shares a habitat with a zebra, an ostrich, and an okapi'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'a keyboard, ipads and recording equipment on a desk'. Find frequency of the letter 'n'

Ex Output:

4