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

Ex Input:
Sentence: 'two elephants facing each other touching trunks in an enclosure'. Find frequency of the letter 'f'

Ex Output:
1

Ex Input:
Sentence: 'a dog has found a rather large stick for playing fetch'. Find frequency of the letter 't'

Ex Output:
3

Ex Input:
Sentence: 'three places at the long table are set for a meal'. Find frequency of the letter 'l'

Ex Output:
4