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

Ex Input:
Sentence: 'the street sign is next to a curved road'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'a bed with a dog laying on it next to two laptop computers'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a white car in front of a stop sign and a group of umbrellas'. Find frequency of the letter 'a'

Ex Output:

6