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

Ex Input:
Sentence: 'people playing wii bowling in a modern library'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'a giraffe sticking it's tongue out near a window'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a woman looking at and pushing buttons on a wii controller'. Find frequency of the letter 's'

Ex Output:

2