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

Ex Input:
Sentence: 'a large grass pasture land with sheep grazing on grass'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'a small white plane sitting on top of the ocean'. Find frequency of the letter 'e'

Ex Output:
4


Ex Input:
Sentence: 'a picture of an airplane getting ready to board'. Find frequency of the letter 'o'

Ex Output:

3