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

Ex Input:
Sentence: 'a young boy holding a piece of paper on top of a table'. Find frequency of the letter 'y'

Ex Output:
2


Ex Input:
Sentence: 'an image of a cautionary construction sign'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a big cow statue standing next to some power lines'. Find frequency of the letter 'o'

Ex Output:

4