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

Ex Input:
Sentence: 'large grassy pasture filled with trees and a single horse'. Find frequency of the letter 'l'

Ex Output:
4


Ex Input:
Sentence: 'two persons standing outside a moving sub train'. Find frequency of the letter 'a'

Ex Output:
3


Ex Input:
Sentence: 'a motorcycle rider dips low as he takes a turn'. Find frequency of the letter 'o'

Ex Output:

3