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

Ex Input:
Sentence: 'a group of people walking down a rain soaked street with umbrellas'. Find frequency of the letter 'w'

Ex Output:
3


Ex Input:
Sentence: 'a plate of food, with broccoli and nuts'. Find frequency of the letter 'b'

Ex Output:
1


Ex Input:
Sentence: 'birds walking at waters edge in the rain'. Find frequency of the letter 'i'

Ex Output:

4