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

Ex Input:
Sentence: 'three elephants walk up a dirt trail from the water'. Find frequency of the letter 'l'

Ex Output:
3


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: 'an old boat on a beach near a large body of water'. Find frequency of the letter 'a'

Ex Output:

8