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

Ex Input:
Sentence: 'man riding a skate board down the little board way'. Find frequency of the letter 'k'

Ex Output:
1


Ex Input:
Sentence: 'a man with headphones on is hunched over a sink while being recorded'. Find frequency of the letter 'd'

Ex Output:
4


Ex Input:
Sentence: 'a street at night, stop lights and cars'. Find frequency of the letter 'r'

Ex Output:

2