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

Ex Input:
Sentence: 'a train on a train track going through a bunch of trees'. Find frequency of the letter 'u'

Ex Output:
2


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

Ex Output:
2


Ex Input:
Sentence: 'a group of people standing around each other having drinks'. Find frequency of the letter 'e'

Ex Output:

4