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

Ex Input:
Sentence: 'a metallic stove top oven inside of a wooden kitchen'. Find frequency of the letter 'v'

Ex Output:
2


Ex Input:
Sentence: 'a person trying to flip a skateboard in a garage'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'two vehicles are parked along a city street'. Find frequency of the letter 'r'

Ex Output:

3