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

Ex Input:
Sentence: 'a man skating down a stair rail in front of a bunch of people'. Find frequency of the letter 'o'

Ex Output:
5


Ex Input:
Sentence: 'a small boat travels on the water next to the shore'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'three mountain goats stand in the middle of a road'. Find frequency of the letter 'e'

Ex Output:

4