1978 AMC 12 Question 4

If $a=1,$ $b=10,$ $c=100$ and $d=1000,$ then $$
\begin{aligned} &(a+b+c-d)+(a+b-c+d)\\ &\quad+(a-b+c+d)\\ &\quad+(-a+b+c+d) \end{aligned}
$$ is equal to