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

Ex Input:
Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a bunch of green bananas is hanging on a tree'. Find frequency of the letter 'n'

Ex Output:
7


Ex Input:
Sentence: 'a red fire hydrant sitting in front of a stucco wall'. Find frequency of the letter 'e'

Ex Output:

2