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

Ex Input:
Sentence: 'a little boy standing near a couch and a table'. Find frequency of the letter 'i'

Ex Output:
2


Ex Input:
Sentence: 'an image of a cautionary construction sign'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a blue train on a track next to another track'. Find frequency of the letter 'c'

Ex Output:

2