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

Ex Input:
Sentence: 'a blue tripocal bird is perched on a wooden fence'. Find frequency of the letter 'd'

Ex Output:
3


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 street filled with red buses next to tall buildings'. Find frequency of the letter 'g'

Ex Output:

1