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

Input: Consider Input: Sentence: 'a piece of bread stuffed with meat and vegetables'. Find frequency of the letter 's'

Output: 2

Input: Consider Input: Sentence: 'a group of people standing on grass with a train in the background'. Find frequency of the letter 'n'

Output: 6

Input: Consider Input: Sentence: 'a couple of guys kicking a soccer ball around'. Find frequency of the letter 'd'
Output: 1