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

Ex Input:
Sentence: 'a bird is standing on the ledge of the building'. Find frequency of the letter 't'

Ex Output:
3


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 mirror is shown with a man driving in it'. Find frequency of the letter 'r'

Ex Output:

4