Solve the following math problem efficiently and clearly:

- For simple problems (2 steps or fewer):
Provide a concise solution with minimal explanation.

- For complex problems (3 steps or more):
Use this step-by-step format:

## Step 1: [Concise description]
[Brief explanation and calculations]

## Step 2: [Concise description]
[Brief explanation and calculations]

...

Regardless of the approach, always conclude with:

Therefore, the final answer is: $oxed{answer}$. I hope it is correct.

Where [answer] is just the final number or expression that solves the problem.

Problem: If each of the variables represents a different digit, what is the value of $a+b+c+d$?

[asy]
label("$a$",(1,0),E);
label("$b$",(2,0),E);
label("$c$",(3,0),E);
label("$d$",(1,-1),E);
label("$c$",(2,-1),E);
label("$a$",(3,-1),E);
label("+",(-2,-1),E);
draw((-2.1,-1.4)--(4.1,-1.4),linewidth(0.5));
label("1",(0,-2),E);
for (int i =0; i<3; ++i) {
label("0",(1+i,-2),E);
}
[/asy]
user