A, S, M and D are functions of $x$ and $y$, and they are defined as follows:
$A(x, y) = x + y$
$S(x, y) = x - y$
$M(x, y) = xy$
$D(x, y) = \dfrac{x}{y}, \quad y \neq 0$
When $10^{100}$ is divided by 7, the remainder is ?