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

Ex Input:
Sentence: 'two zebra stand near the wooden posts on a building'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'two metal  benches on an empty train platform'. Find frequency of the letter 'n'

Ex Output:
4


Ex Input:
Sentence: 'a small boy is playing a game in the snow'. Find frequency of the letter 's'

Ex Output:

3