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

Ex Input:
Sentence: 'a doorway looking into a small bathroom with white toilet'. Find frequency of the letter 'r'

Ex Output:
2


Ex Input:
Sentence: 'two zebra stand near the wooden posts on a building'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'a group of snowboarders posing with their snowboards'. Find frequency of the letter 'w'

Ex Output:

3