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

Input: Consider Input: Sentence: 'a man opening up a package sitting on a couch'. Find frequency of the letter 'n'

Output: 5

Input: Consider Input: Sentence: 'two people are riding on canoes down a river'. Find frequency of the letter 'e'

Output: 5

Input: Consider Input: Sentence: 'two brown grizzly bears playing in the water'. Find frequency of the letter 'i'
Output: 3