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

Ex Input:
Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a bowl of granola, dried fruit, and bananas'. Find frequency of the letter 'u'

Ex Output:
1


Ex Input:
Sentence: 'baseball batter waiting on a pitch as catcher signals and umpire watches'. Find frequency of the letter 'b'

Ex Output:

3