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

Ex Input:
Sentence: 'black and white photograph of man and woman sitting on a bench'. Find frequency of the letter 'w'

Ex Output:
2


Ex Input:
Sentence: 'guy leans on truck's hood while taking pics next to parked motorcycles'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'a long train is going down the tracks over a bridge'. Find frequency of the letter 'v'

Ex Output:

1