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

Ex Input:
Sentence: 'a small boat travels on the water next to the shore'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a photo of a couple of people at a convention'. Find frequency of the letter 'v'

Ex Output:
1


Ex Input:
Sentence: 'a baseball player holding a base on a field'. Find frequency of the letter 'b'

Ex Output:

3