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

Ex Input:
Sentence: 'a young elephant is touching a bigger elephant with its trunk'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'a person riding a surfboard in the middle of a wave'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'a cat sitting on the armrest of a couch'. Find frequency of the letter 'o'

Ex Output:

3