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

Input: Consider Input: Sentence: 'a green bus driving in a street filled with heavy traffic'. Find frequency of the letter 'v'

Output: 2


Input: Consider Input: Sentence: 'a bus is driving on the street behind some cars'. Find frequency of the letter 'a'

Output: 2


Input: Consider Input: Sentence: 'two people wearing snowboards sitting on a snowy slope'. Find frequency of the letter 's'


Output: 5