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

Ex Input:
Sentence: 'silhouette of person playing frisbee with moutain and sunset'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'there is a zebra that is walking enar a car'. Find frequency of the letter 'r'

Ex Output:
4


Ex Input:
Sentence: 'a red double decker bus driving on a city street'. Find frequency of the letter 'b'

Ex Output:

2