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

Input: Consider Input: Sentence: 'a red and white train passing a train station'. Find frequency of the letter 'a'

Output: 7


Input: Consider Input: Sentence: 'a yellow fire hydrant in the forefront of a roadway'. Find frequency of the letter 'r'

Output: 5


Input: Consider Input: Sentence: 'three people ride their horses down a beach'. Find frequency of the letter 's'


Output: 2