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

Ex Input:
Sentence: 'a dog laying on the back of a boat in the water'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'an old boat on a beach near a large body of water'. Find frequency of the letter 'a'

Ex Output:
8


Ex Input:
Sentence: 'a boy is about to launch himself off the side of a skateboard ramp'. Find frequency of the letter 'e'

Ex Output:

4