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

Ex Input:
Sentence: 'a surfer is in the middle of an ocean wave'. Find frequency of the letter 'i'

Ex Output:
3


Ex Input:
Sentence: 'apples, pears, and oranges are piled up for sale'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'a red stop sign sitting on the side of a street'. Find frequency of the letter 's'

Ex Output:

5