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

Ex Input:
Sentence: 'a bus is driving on the street behind some cars'. Find frequency of the letter 'a'

Ex Output:
2


Ex Input:
Sentence: 'a young man riding a skateboard near a forest'. Find frequency of the letter 'd'

Ex Output:
2


Ex Input:
Sentence: 'a cat sleeping near lots of pairs of shoes'. Find frequency of the letter 'r'

Ex Output:

2