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

Ex Input:
Sentence: 'statues of 2 zebras and 1 giraffe in a doorway'. Find frequency of the letter 'a'

Ex Output:
6


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: 'two electric toothbrush heads laying on some tools'. Find frequency of the letter 'l'

Ex Output:

3