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

Ex Input:
Sentence: 'flower in a vase full of water sitting on a stand '. Find frequency of the letter 'l'

Ex Output:
3


Ex Input:
Sentence: 'a man riding a white surfboard on a large wave'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'the giraffe is standing beside a wire fence'. Find frequency of the letter 'i'

Ex Output:

5