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

Ex Input:
Sentence: 'a surfer is in the middle of an ocean wave'. Find frequency of the letter 'i'

Ex Output:
3


Ex Input:
Sentence: 'a girl that has a kite in the air'. Find frequency of the letter 'r'

Ex Output:
2


Ex Input:
Sentence: 'a cat that is standing in a dish while eating food'. Find frequency of the letter 's'

Ex Output:

3