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

Input: Consider Input: Sentence: 'a black computer with a screen reading "press any key to begin."'. Find frequency of the letter 'a'

Output: 5

Input: Consider Input: Sentence: 'a dog has found a rather large stick for playing fetch'. Find frequency of the letter 't'

Output: 3

Input: Consider Input: Sentence: 'living room with white walls and a wooden floor'. Find frequency of the letter 'l'
Output: 4