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

Ex Input:
Sentence: 'a blue tripocal bird is perched on a wooden fence'. Find frequency of the letter 'd'

Ex Output:
3


Ex Input:
Sentence: 'a closet with a fan, luggage and various boxes'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'a large pizza sitting on top of a pan covered in cheese'. Find frequency of the letter 't'

Ex Output:

3