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 woman walking on a shore next to a river'. Find frequency of the letter 'v'

Ex Output:
1


Ex Input:
Sentence: 'the display at a shop with a stuffed animal wearing a hat'. Find frequency of the letter 'u'

Ex Output:

1