Golden Plate

你有一个盘子，你想在上面加些镀金。板是一个长方形，我们把它分成W×H单元。应该有K个要被金属的格子，第一个应该沿着板的边缘，第二个远离边缘2格，第三个4格等。每个环都有一个1格的宽度。这些环的第I个应该包括所有在其中心面积为（W−4（I−1））×（H−4（I−1））矩形中心在边缘上的格子 输入 W,H,K 输出 被镀金的格子数（一定要有换行！！！）

You have a plate and you want to add some gilding to it. The plate is a rectangle that we split into $ w\times h $ cells. There should be $ k $ gilded rings, the first one should go along the edge of the plate, the second one — $ 2 $ cells away from the edge and so on. Each ring has a width of $ 1 $ cell. Formally, the $ i $ -th of these rings should consist of all bordering cells on the inner rectangle of size $ (w - 4(i - 1))\times(h - 4(i - 1)) $ . The picture corresponds to the third example.Your task is to compute the number of cells to be gilded.

The only line contains three integers $ w $ , $ h $ and $ k $ ( $ 3 \le w, h \le 100 $ , $ 1 \le k \le \left\lfloor \frac{min(n, m) + 1}{4}\right\rfloor $ , where $ \lfloor x \rfloor $ denotes the number $ x $ rounded down) — the number of rows, columns and the number of rings, respectively.

Print a single positive integer — the number of cells to be gilded.

3 3 1

8

7 9 1

28

7 9 2

40

The first example is shown on the picture below. The second example is shown on the picture below. The third example is shown in the problem description.