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

Input: Consider Input: Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'

Output: 5


Input: Consider Input: Sentence: 'pedestrians pass by a stop sign, some holding surfboards'. Find frequency of the letter 'n'

Output: 3


Input: Consider Input: Sentence: 'a bunch of old phones on the ground chained up'. Find frequency of the letter 'o'


Output: 5