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

Ex Input:
Sentence: 'a laptop computer with pictures of giraffes on the homescreen'. Find frequency of the letter 'o'

Ex Output:
5


Ex Input:
Sentence: 'a glass bowl of raw broccoli, a ceramic bowl of raw green chili peppers, and steel bowl of raw daikon'. Find frequency of the letter 'a'

Ex Output:
9


Ex Input:
Sentence: 'a woman riding a skateboard in a puddle of water'. Find frequency of the letter 'w'

Ex Output:

2