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: 'hand holding a white calculator inside a store'. Find frequency of the letter 'o'

Ex Output:
3

Ex Input:
Sentence: 'there are two giraffes standing together behind a small fence'. Find frequency of the letter 'h'

Ex Output:
3