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

Input: Consider Input: Sentence: 'a commuter bus in england by a clock tower building'. Find frequency of the letter 'w'

Output: 1

Input: Consider Input: Sentence: 'a black animal in dirt area below trees and rocks'. Find frequency of the letter 'n'

Output: 3

Input: Consider Input: Sentence: 'this is a short person running with a checkerboard kite'. Find frequency of the letter 'c'
Output: 2