Symmetric Matrices & Quadratic Forms · Easy problem

The positive definiteness test for $A = \begin{pmatrix}2 & 1 & 0\\1 & 2 & 1\\0 & 1 & 2\end{pmatrix}$ uses its leading principal minors $d_1, d_2, d_3$ (the determinants of the upper-left $1\times 1$, $2\times 2$ and $3\times 3$ blocks). Find $d_3$.