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

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

Ex Output:
2


Ex Input:
Sentence: 'some giraffes moving across a big grass field'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'a big clock built inside of a building'. Find frequency of the letter 'l'

Ex Output:

3