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 passenger bus that is driving down the street'. Find frequency of the letter 'r'

Ex Output:
3


Ex Input:
Sentence: 'a white bowl of oranges on a table'. Find frequency of the letter 'b'

Ex Output:

2