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

Ex Input:
Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'

Ex Output:
2


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: 'statute of a horse and rider on top of a block wall'. Find frequency of the letter 'a'

Ex Output:

5