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

Input: Consider Input: Sentence: 'a person is holding a chocolate doughnut with rainbow sprinkles'. Find frequency of the letter 's'

Output: 4

Input: Consider Input: Sentence: 'several zebras and a giraffe in an enclosure'. Find frequency of the letter 's'

Output: 3

Input: Consider Input: Sentence: 'a dog running with a frisbee in its mouth'. Find frequency of the letter 'd'
Output: 1