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

Ex Input:
Sentence: 'two people are riding on canoes down a river'. Find frequency of the letter 'e'

Ex Output:
5

Ex Input:
Sentence: 'city two way street with cars lined up on both sides'. Find frequency of the letter 'h'

Ex Output:
2

Ex Input:
Sentence: 'the skateboarder is jumping over a huge statue of a shoe'. Find frequency of the letter 'i'

Ex Output:
2