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

Ex Input:
Sentence: 'a toilet sits in a cluttered bathroom next to a sink'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a small white plane sitting on top of the ocean'. Find frequency of the letter 'e'

Ex Output:
4


Ex Input:
Sentence: 'an image  of a professional baseball game being played'. Find frequency of the letter 'a'

Ex Output:

8