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

Ex Input:
Sentence: 'a man in costume talking on a cell phone'. Find frequency of the letter 'm'

Ex Output:
2


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 dog is laying down on a bed'. Find frequency of the letter 'n'

Ex Output:

3