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

Ex Input:
Sentence: 'a small boat travels on the water next to the shore'. Find frequency of the letter 'a'

Ex Output:
5

Ex Input:
Sentence: 'a bowl of vegetables in a soup like substance next to a spoon'. Find frequency of the letter 'a'

Ex Output:
5

Ex Input:
Sentence: 'people waiting on a train platform in a wooded area'. Find frequency of the letter 'p'

Ex Output:
3