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

Input: Consider Input: Sentence: 'a small boy in a high chair eating a cupcake'. Find frequency of the letter 'i'

Output: 4

Input: Consider Input: Sentence: 'the skateboarder has on red and black sneakers and is riding a skateboard'. Find frequency of the letter 'g'

Output: 1

Input: Consider Input: Sentence: 'a bathroom with a toilet and a stand up shower'. Find frequency of the letter 's'
Output: 2