Let $M$ and $N$ are two non singular matrices of order $3$ with real entries such that $\left(adj\mathrm{}\mathrm{}M\right)=2N$ and $\left(adj\mathrm{}\mathrm{}N\right)=M$. If $MN=\lambda \mathrm{{\rm I}}$, then the value of $\lambda$ is equal to (where, $\left(adjX\right)$ represents the adjoint matrix of matrix $X$ and $\mathrm{I}$ represents an identity matrix)