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

Ex Input:
Sentence: 'a cat sprawls out and sleeps on its back on a lounge chair with an acorn theme'. Find frequency of the letter 'r'

Ex Output:
3


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 pizza sitting on a table, on a white plate'. Find frequency of the letter 't'

Ex Output:

5