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

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 red and white train passing a train station'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'a cooked pizza on a silver platter with another in the background'. Find frequency of the letter 'e'

Ex Output:

5