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

Ex Input:
Sentence: 'a couple of men standing inside of a liquor store'. Find frequency of the letter 'p'

Ex Output:
1


Ex Input:
Sentence: 'a group of tennis players on a tennis court'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'a photographer holding a camera is looking in a mirror'. Find frequency of the letter 'n'

Ex Output:

3