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 woman at a table checking her cell phone'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'men standing in the grass with a frisbee'. Find frequency of the letter 'a'

Ex Output:

3