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

Ex Input:
Sentence: 'a bird in a tree looking up at branches'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'a log in the water with three birds perched on it'. Find frequency of the letter 'r'

Ex Output:
4


Ex Input:
Sentence: 'a red stop sign sitting on the side of  a road'. Find frequency of the letter 'i'

Ex Output:

4