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

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

Ex Output:
3


Ex Input:
Sentence: 'two men are playing a video game as another sits watching'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'an image taken in a car of two green traffic lights'. Find frequency of the letter 'g'

Ex Output:

3