A7909. Repaintings

A chessboard $n×m$ in size is given. During the zero minute we repaint all the black squares to the 0 color. During the $i$ -th minute we repaint to the $i$ color the initially black squares that have exactly four corner-adjacent squares painted $i-1$ (all such squares are repainted simultaneously). This process continues ad infinitum. You have to figure out how many squares we repainted exactly $x$ times.

The upper left square of the board has to be assumed to be always black. Two squares are called corner-adjacent, if they have exactly one common point.

The first line contains integers $n$ and $m$ ( $1<=n,m<=5000$ ). The second line contains integer $x$ ( $1<=x<=10^{9}$ ).

Print how many squares will be painted exactly $x$ times.