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

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: 'a bowl of granola with raspberries and honey on top with a spoon'. Find frequency of the letter 'w'

Ex Output:
3


Ex Input:
Sentence: 'a large herd of zebras are in the grass together'. Find frequency of the letter 'i'

Ex Output:

1