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

Ex Input:
Sentence: 'a man serving himself pizza in a wooden booth'. Find frequency of the letter 'n'

Ex Output:
4


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: 'group in darklit room talking and looking at their cell phones holding wine glasses'. Find frequency of the letter 'i'

Ex Output:

7