CF1034B Little C Loves 3 II

**题目大意：** 给定一个$n\times m$的棋盘，每次可以在上面放一对棋子$(x,y)(x',y')$，要求$\mid x-x'\mid+\mid y-y'\mid==3$，问最多可以放多少**个**棋子

一行两个整数$n,m$

一个整数，表示最多能放多少个棋子

In the first example, the Manhattan distance between any two cells is smaller than $ 3 $ , so the answer is $ 0 $ . In the second example, a possible solution is $ (1,1)(3,2) $ , $ (1,2)(3,3) $ , $ (2,1)(1,3) $ , $ (3,1)(2,3) $ .