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 row of vintage cars in a grassy field'. Find frequency of the letter 'v'

Ex Output:
1


Ex Input:
Sentence: 'a man flying into the air as he catches a frisbee'. Find frequency of the letter 'c'

Ex Output:

2