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 lady is standing near a luggage stand at the air port'. Find frequency of the letter 'a'

Ex Output:
9


Ex Input:
Sentence: 'a large passenger jet flying through the sky filled with smog'. Find frequency of the letter 'r'

Ex Output:

3