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

Ex Input:
Sentence: 'a police officer who is riding on a horse'. Find frequency of the letter 'p'

Ex Output:
1

Ex Input:
Sentence: 'a plastic plastic plate topped with three different type of food'. Find frequency of the letter 'l'

Ex Output:
3

Ex Input:
Sentence: 'woman intently plays wii in her living room'. Find frequency of the letter 'w'

Ex Output:
2