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

Ex Input:
Sentence: 'an old glass vase containing flowers on a glass table'. Find frequency of the letter 'b'

Ex Output:
1


Ex Input:
Sentence: 'a white paper plate with a slice of pizza on it'. Find frequency of the letter 'h'

Ex Output:
2


Ex Input:
Sentence: 'a person riding on the back of a brown horse on a rocky hillside'. Find frequency of the letter 'a'

Ex Output:

4