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

Input: Consider Input: Sentence: 'a traffic signal by a wire filled with some birds'. Find frequency of the letter 'e'

Output: 3

Input: Consider Input: Sentence: 'a couple of boys in a field playing baseball'. Find frequency of the letter 'i'

Output: 3

Input: Consider Input: Sentence: 'a young couple all dressed up for a formal event'. Find frequency of the letter 'e'
Output: 5