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

Ex Input:
Sentence: 'three woman are having a discussion in the kitchen'. Find frequency of the letter 'n'

Ex Output:
5


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

Ex Output:
4


Ex Input:
Sentence: 'a living room filled with furniture and surrounded by windows'. Find frequency of the letter 'r'

Ex Output:

5