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

Ex Input:
Sentence: 'two men are playing a video game as another sits watching'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'a railroad train pulling up to the train platform'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'large assortment of vegetables displayed for sale on large round table'. Find frequency of the letter 'u'

Ex Output:

1