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

Ex Input:
Sentence: 'a guy surfs a wave with his surfboard'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'a photo of a toilet which is not clean'. Find frequency of the letter 'w'

Ex Output:
1


Ex Input:
Sentence: 'attic bedroom with a rocking chair and spindled bed'. Find frequency of the letter 'o'

Ex Output:

3