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

Ex Input:
Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'

Ex Output:
3

Ex Input:
Sentence: 'a woman holds the reins of a saddled horse'. Find frequency of the letter 'm'

Ex Output:
1

Ex Input:
Sentence: 'a bathroom shot inside of a bathroom'. Find frequency of the letter 'h'

Ex Output:
3