Sum of Squared Eigenvalues

Let $\lambda_1$, $\lambda_2$, and $\lambda_3$ be the eigenvalues of matrix $$M=\begin{pmatrix} 1 & 2 & 3\\ 4 & 5 & 6\\ 7 & 8& 9 \end{pmatrix}$$Find the value of $\lambda_1^2 +\lambda_2^2 + \lambda_3^2$.