CF508A.Pasha and Pixels

Pasha loves his phone and also putting his hair up... But the hair is now irrelevant.

Pasha has installed a new game to his phone. The goal of the game is following. There is a rectangular field consisting of n row with m pixels in each row. Initially, all the pixels are colored white. In one move, Pasha can choose any pixel and color it black. In particular, he can choose the pixel that is already black, then after the boy's move the pixel does not change, that is, it remains black. Pasha loses the game when a 2 × 2 square consisting of black pixels is formed.

Pasha has made a plan of k moves, according to which he will paint pixels. Each turn in his plan is represented as a pair of numbers i and j, denoting respectively the row and the column of the pixel to be colored on the current move.

Determine whether Pasha loses if he acts in accordance with his plan, and if he does, on what move the 2 × 2 square consisting of black pixels is formed.

帕沙很喜欢他的手机，也喜欢把头发扎起来……不过现在头发已经不重要了。

帕沙在他的手机上安装了一款新游戏。游戏的目标如下：有一个由 $n$ 行组成的矩形区域，每行包含 $m$ 个像素点。初始时，所有像素点均为白色。在一次操作中，帕沙可以选择任意一个像素点并将其涂黑。特别地，他也可以选择一个已经是黑色的像素点；此时，经过该次操作后，该像素点颜色不变，仍为黑色。当出现一个由黑色像素点构成的 $2 \times 2$ 正方形时，帕沙即输掉游戏。

帕沙已制定了一份共 $k$ 步的操作计划，按此计划依次给像素点上色。计划中的每一步用一对数 $i$ 和 $j$ 表示，分别代表当前要涂黑的像素点所在的行号和列号。

请判断：若帕沙严格按照该计划执行操作，他是否会输掉游戏？若会，则是在第几步操作后首次形成由黑色像素点构成的 $2 \times 2$ 正方形？

The first line of the input contains three integers n, m, k (1 ≤ n, m ≤ 1000, 1 ≤ k ≤ 105) — the number of rows, the number of columns and the number of moves that Pasha is going to perform.

The next k lines contain Pasha's moves in the order he makes them. Each line contains two integers i and j (1 ≤ i ≤ n, 1 ≤ j ≤ m), representing the row number and column number of the pixel that was painted during a move.

输入的第一行包含三个整数 $n$、$m$、$k$（$1 \leq n, m \leq 1000$，$1 \leq k \leq 10^5$）—— 分别表示网格的行数、列数以及 Pasha 即将执行的操作次数。

接下来的 $k$ 行按操作顺序给出 Pasha 的每次操作。每行包含两个整数 $i$ 和 $j$（$1 \leq i \leq n$，$1 \leq j \leq m$），表示该次操作所涂色像素所在的行号与列号。

If Pasha loses, print the number of the move when the 2 × 2 square consisting of black pixels is formed.

If Pasha doesn't lose, that is, no 2 × 2 square consisting of black pixels is formed during the given k moves, print 0.

如果帕沙输了，输出形成由黑色像素组成的 $2 \times 2$ 方块时的步数。

如果帕沙没有输，即在给定的 $k$ 步内未形成任何由黑色像素组成的 $2 \times 2$ 方块，则输出 0。