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

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

Ex Output:
3


Ex Input:
Sentence: 'a young man with glasses on is taking a big bite'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'an old plane is parked outside of a large building'. Find frequency of the letter 'l'

Ex Output:

4