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

Input: Consider Input: Sentence: 'the large modern train is on the train track'. Find frequency of the letter 'm'

Output: 1

Input: Consider Input: Sentence: 'a large grass pasture land with sheep grazing on grass'. Find frequency of the letter 'a'

Output: 7

Input: Consider Input: Sentence: 'a wooden chair sitting on a sidewalk next to a tree'. Find frequency of the letter 'w'
Output: 2