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

Ex Input:
Sentence: 'a sailboat is floating near the rocky shore of a beach'. Find frequency of the letter 'o'

Ex Output:
5

Ex Input:
Sentence: 'tow birds flying by a long necked crane'. Find frequency of the letter 'f'

Ex Output:
1

Ex Input:
Sentence: 'the are looking at a deep dish pizza with a slice removed'. Find frequency of the letter 'e'

Ex Output:
7