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

Ex Input:
Sentence: 'a white bathroom sink sitting next to a toilet'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'a black cat laying down on a bed'. Find frequency of the letter 'y'

Ex Output:
1


Ex Input:
Sentence: 'two colorful parrots perched on a tree branch'. Find frequency of the letter 'o'

Ex Output:

5