In this task, you need to replace a letter in the sentence with another given letter.

Input: Consider Input: Sentence: 'a person on a snow board flying through the air'. Replace the letter 'f' with 'n' in the sentence.

Output: a person on a snow board nlying through the air

Input: Consider Input: Sentence: 'a small bird perched on some thin branches'. Replace the letter 'a' with 'f' in the sentence.

Output: f smfll bird perched on some thin brfnches

Input: Consider Input: Sentence: 'a small dog and a medium sized dog are greeting each other'. Replace the letter 'e' with 'y' in the sentence.
Output: a small dog and a mydium sizyd dog ary gryyting yach othyr