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: 'the street sign is next to a curved road'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'one news anchor looks angry while the other looks concerned about the large cat story they're talking about'. Find frequency of the letter 's'

Ex Output:

4