For the matrix $A = \begin{pmatrix} 1 & 2 & 3 \\ 4 & 5 & 6 \\ 7 & 8 & 9 \end{pmatrix}$, what is the minor $M_{1,1}$ (the determinant of the $2 \times 2$ submatrix obtained by deleting row 1 and column 1)?