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

Ex Input:
Sentence: 'a close up of a train on a track in the dark'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'a truck is parked in front of a store'. Find frequency of the letter 't'

Ex Output:
3


Ex Input:
Sentence: 'a woman posing for a camera in ski gear near mountains'. Find frequency of the letter 'i'

Ex Output:

4