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

Ex Input:
Sentence: 'a giraffe shares a habitat with a zebra, an ostrich, and an okapi'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'an area that has surrounded by a metal fence'. Find frequency of the letter 'o'

Ex Output:
1


Ex Input:
Sentence: 'a horse bending it's neck to eat hay in a caged in area'. Find frequency of the letter 'd'

Ex Output:

2