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

Ex Input:
Sentence: 'two zebras feed on a plant through some wire mesh'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'two people wearing snowboards sitting on a snowy slope'. Find frequency of the letter 's'

Ex Output:
5


Ex Input:
Sentence: 'there is a phone, computer, papers, and drink on this desk'. Find frequency of the letter 's'

Ex Output:

4