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

Ex Input:
Sentence: 'statues of 2 zebras and 1 giraffe in a doorway'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'town clocks affixed to a tall, brick building'. Find frequency of the letter 'r'

Ex Output:
1


Ex Input:
Sentence: 'a cow with a ring in its nose is being lead by its owner'. Find frequency of the letter 'a'

Ex Output:

3