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

Ex Input:
Sentence: 'a person is performing a stunt on a snowboard'. Find frequency of the letter 'p'

Ex Output:
2


Ex Input:
Sentence: 'a microwave oven with a yellow note on the door'. Find frequency of the letter 'w'

Ex Output:
3


Ex Input:
Sentence: 'a baseball player sliding to the base to avoid being tagged'. Find frequency of the letter 'a'

Ex Output:

7