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

Ex Input:
Sentence: 'a half eaten doughnut in a persons hand'. Find frequency of the letter 'h'

Ex Output:
3


Ex Input:
Sentence: 'a white and blue plate topped with meat and a salad'. Find frequency of the letter 'u'

Ex Output:
1


Ex Input:
Sentence: 'a young man riding skis through a snow covered forest'. Find frequency of the letter 'r'

Ex Output:

4