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

Ex Input:
Sentence: 'a commuter bus in england by a clock tower building'. Find frequency of the letter 'w'

Ex Output:
1


Ex Input:
Sentence: 'a dog sitting in the back of a truck flat bed'. Find frequency of the letter 'h'

Ex Output:
1


Ex Input:
Sentence: 'a red refrigerator freezer sitting inside of a kitchen'. Find frequency of the letter 'r'

Ex Output:

7