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

Ex Input:
Sentence: 'a white bathroom sink sitting next to a toilet'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'a man standing on a tennis court holding a racquet'. Find frequency of the letter 's'

Ex Output:
2


Ex Input:
Sentence: 'a person with a cake standing in a room'. Find frequency of the letter 'k'

Ex Output:

1