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

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

Ex Output:
3


Ex Input:
Sentence: 'a man swinging a bat while playing baseball'. Find frequency of the letter 'm'

Ex Output:
1


Ex Input:
Sentence: 'a yellow jeep with a surfboard on top sitting in the sand'. Find frequency of the letter 'a'

Ex Output:

4