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

Ex Input:
Sentence: 'a crowd of people standing in front of a green train'. Find frequency of the letter 'g'

Ex Output:
2


Ex Input:
Sentence: 'town clocks affixed to a tall, brick building'. Find frequency of the letter 'r'

Ex Output:
1


Ex Input:
Sentence: 'two young ladies that are dancing in the room together'. Find frequency of the letter 'a'

Ex Output:

4