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

Ex Input:
Sentence: 'a crooked street sign on a damaged sidewalk'. Replace the letter 'm' with 'u' in the sentence.

Ex Output:
a crooked street sign on a dauaged sidewalk


Ex Input:
Sentence: 'a couple walking down a sidewalk next to some graffiti'. Replace the letter 'a' with 'y' in the sentence.

Ex Output:
y couple wylking down y sidewylk next to some gryffiti


Ex Input:
Sentence: 'a very big building with so many windows'. Replace the letter 'b' with 'a' in the sentence.

Ex Output:

a very aig auilding with so many windows