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

Ex Input:
Sentence: 'this yellow fire hydrant sits in a grass field'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'the sun goes down over a bike tied to a bench at the beach'. Find frequency of the letter 't'

Ex Output:
5


Ex Input:
Sentence: 'a red building with a crowd of people outside it near the water'. Find frequency of the letter 'e'

Ex Output:

7