Two Flowers

Chef Go has planted a flower field — a grid with $n$ rows and $m$ columns. In each cell of this grid, a single flower is planted; let's denote the type of the flower planted in cell $(i, j)$ by $a_{i,j}$. Today, Chef Go is going to make a new menu with two dishes: *Tom Yum Goong* and *Tom Kha Kai*. He needs to pick as many flowers as possible to decorate the dishes and make them look attractive.