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 group of cows that are standing in the grass'. Find frequency of the letter 'g'

Ex Output:
3


Ex Input:
Sentence: 'a man sitting alone at a picnic table with a laptop'. Find frequency of the letter 'a'

Ex Output:

8