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

Ex Input:
Sentence: 'some cubbies with towels in a blue bathroom'. Find frequency of the letter 'l'

Ex Output:
2


Ex Input:
Sentence: 'a large cooked pizza on a dining table'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a train engine on railroad tracks with a person walking near the track'. Find frequency of the letter 'a'

Ex Output:

9