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

Ex Input:
Sentence: 'man in red shirt with black suitcase standing outside of building'. Find frequency of the letter 'i'

Ex Output:
8


Ex Input:
Sentence: 'a downhill skier with snow plumes behind them'. Find frequency of the letter 'i'

Ex Output:
4


Ex Input:
Sentence: 'several boats docked on the marina with passengers wating'. Find frequency of the letter 'a'

Ex Output:

6