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

Input: Consider Input: Sentence: 'a man that is on his cell phone'. Find frequency of the letter 's'

Output: 2


Input: Consider Input: Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'

Output: 2


Input: Consider Input: Sentence: 'a boy is standing in an empty kitchen in front of an open area'. Find frequency of the letter 'n'


Output: 9