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

Ex Input:
Sentence: 'a snowboarder making a jump of a snowy ledge'. Find frequency of the letter 'o'

Ex Output:
4

Ex Input:
Sentence: 'a blue tripocal bird is perched on a wooden fence'. Find frequency of the letter 'd'

Ex Output:
3

Ex Input:
Sentence: 'close up view of an adult colorful parrot'. Find frequency of the letter 'u'

Ex Output:
3