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 crowd of fans watch soccer players from stadium seating'. Find frequency of the letter 'f'

Ex Output:
3


Ex Input:
Sentence: 'a woman sits at a glass table wearing a hat as she holds up a wine glass'. Find frequency of the letter 's'

Ex Output:

9