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

Input: Consider Input: Sentence: 'wooden and black bench on the side of the road'. Find frequency of the letter 'a'

Output: 3

Input: Consider Input: Sentence: 'a person standing operating a cell phone in a room'. Find frequency of the letter 'n'

Output: 6

Input: Consider Input: Sentence: 'an airplane sitting on the tarmac under a night sky'. Find frequency of the letter 'n'
Output: 6