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

Ex Input:
Sentence: 'a person on a skateboard going down a ramp'. Find frequency of the letter 'n'

Ex Output:
4


Ex Input:
Sentence: 'a man sitting in front of a laptop computer next to a child'. Find frequency of the letter 'e'

Ex Output:
2


Ex Input:
Sentence: 'a young man in a blue shirt sitting at a desk'. Find frequency of the letter 'i'

Ex Output:

4