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

Ex Input:
Sentence: 'pedestrian in stripe clothing standing on street corner'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'person wearing all white leaned up against a wall with a yellow sign'. Find frequency of the letter 'a'

Ex Output:
8


Ex Input:
Sentence: 'a couple of men riding skis on a snow covered slope'. Find frequency of the letter 'p'

Ex Output:

2