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

Ex Input:
Sentence: 'a bunch of broken down trains sit in a yard'. Find frequency of the letter 'n'

Ex Output:
5


Ex Input:
Sentence: 'a dog has found a rather large stick for playing fetch'. Find frequency of the letter 't'

Ex Output:
3


Ex Input:
Sentence: 'a black and white zebra looks like it's made of legos'. Find frequency of the letter 'd'

Ex Output:

2