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

Ex Input:
Sentence: 'hotel towels with sunglasses perched and hotel business cards and catalog'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'person wearing all white leaned up against a wall with a yellow sign'. Find frequency of the letter 'a'

Ex Output:
8


Ex Input:
Sentence: 'a large jet airplane sitting on a runway with dark clouds in the background'. Find frequency of the letter 'r'

Ex Output:

5