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

Ex Input:
Sentence: 'a stop sign near a rail road crossing sign'. Find frequency of the letter 'g'

Ex Output:
3


Ex Input:
Sentence: 'a little boy standing near a couch and a table'. Find frequency of the letter 'i'

Ex Output:
2


Ex Input:
Sentence: 'a truck with a camper sits parked in some vegetation'. Find frequency of the letter 's'

Ex Output:

3