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

Input: Consider Input: Sentence: 'a young man with glasses on is taking a big bite'. Find frequency of the letter 's'

Output: 4

Input: Consider Input: Sentence: 'a group of giraffes walk together by a hill'. Find frequency of the letter 'b'

Output: 1

Input: Consider Input: Sentence: 'a close up on a cows head in a pen'. Find frequency of the letter 'n'
Output: 3