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

Ex Input:
Sentence: 'a man flying through the air on top of a skateboard'. Find frequency of the letter 'r'

Ex Output:
3


Ex Input:
Sentence: 'a bunch of fruit sitting in a bowl, its overflowing'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'a bear sitting down on top of several rocks'. Find frequency of the letter 'r'

Ex Output:

3