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: 'young girl playing with refrigerator magnet while kneeling on floor'. Find frequency of the letter 'n'

Ex Output:
6

Ex Input:
Sentence: 'a baseball pitcher on the mount mid pitch'. Find frequency of the letter 'c'

Ex Output:
2