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

Input: Consider Input: Sentence: 'a surfer is in the middle of an ocean wave'. Find frequency of the letter 'i'

Output: 3

Input: Consider Input: Sentence: 'a girl that has a kite in the air'. Find frequency of the letter 'r'

Output: 2

Input: Consider Input: Sentence: 'a group of people wearing cold weather attire, backpacks and skies, follow eachother'. Find frequency of the letter 's'
Output: 3