  Starting from a divergence-free rank-4 tensor of which the trace is the
cosmological Einstein tensor, we give a construction of conserved charges in
Einstein's gravity and its higher derivative extensions for asymptotically
anti-de Sitter spacetimes. The current yielding the charge is explicitly
gauge-invariant, and the charge expression involves the linearized Riemann
tensor at the boundary. Hence, to compute the mass and angular momenta in these
spacetimes, one just needs to compute the linearized Riemann tensor. We give
two examples.
