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

Ex Input:
Sentence: 'a man with glasses adjusting his tie in a mirror'. Find frequency of the letter 's'

Ex Output:
5


Ex Input:
Sentence: 'a man in a black shirt prepares to catch a frisbee'. Find frequency of the letter 'f'

Ex Output:
1


Ex Input:
Sentence: 'a person is taking a picture of their self while brushing their teeth'. Find frequency of the letter 'a'

Ex Output:

3