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

Ex Input:
Sentence: 'a toasted sub sandwich is next to a salad'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'a red train traveling down train tracks near a forest'. Find frequency of the letter 'f'

Ex Output:
1


Ex Input:
Sentence: 'there are wood benches lining a path to the lighthouse'. Find frequency of the letter 'l'

Ex Output:

2