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

Ex Input:
Sentence: 'some sheep are standing in a grassy field'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a pizza is in a box on a table outside'. Find frequency of the letter 'u'

Ex Output:
1


Ex Input:
Sentence: 'a street sign stating to drive slow due to turtle crossing'. Find frequency of the letter 'e'

Ex Output:

5