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

Ex Input:
Sentence: 'a young girl skiing down a snowy mountain'. Find frequency of the letter 'l'

Ex Output:
1


Ex Input:
Sentence: 'a man paddle boarding by a boat dock in a city'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'a black bird perched on a wire next to a tree'. Find frequency of the letter 'n'

Ex Output:

2