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

Ex Input:
Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a man on stiltz is standing under a pink umbrella'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'the men sit at the table with books in front of them'. Find frequency of the letter 't'

Ex Output:

8