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

Ex Input:
Sentence: 'a picture of two men on a motorcycle in front of a railroad track'. Find frequency of the letter 'n'

Ex Output:
4


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

Ex Output:
3


Ex Input:
Sentence: 'the adult and the group of children wearing skis all extend their hands upward'. Find frequency of the letter 'e'

Ex Output:

7