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

Ex Input:
Sentence: 'a person is riding in a cart pulled by a horse'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a group of people standing on grass with a train in the background'. Find frequency of the letter 'n'

Ex Output:
6


Ex Input:
Sentence: 'the side of a white house situated at the point of an intersection'. Find frequency of the letter 'd'

Ex Output:

2