1

import java.util.Scanner;

public class stones {

    static int M, N, i, p = 3;
    static boolean finished;

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        N = scanner.nextInt();
        M = scanner.nextInt();
        int[] stones = new int[N * M];
        int R = scanner.nextInt();
        String[] splitOne = null;
        i = 1;

        scanner.nextLine();

        finished = false;

        String Right[] = new String[R];

        for (int i = 0; i < R-1; i++) {
            Right[i] = scanner.nextLine();
        }

        int j = 0;

        while (!finished) {
            splitOne = Right[j].split(" ");

            int[] splitFinal = new int[2];

            splitFinal[0] = Integer.parseInt(splitOne[0]);
            splitFinal[1] = Integer.parseInt(splitOne[1]);

            insert(stones, splitFinal[0], splitFinal[1]);
            j++;
            i++;
        }
    }

    private static void isFinished(int thisNumber, int coordination) {
        if (thisNumber == 1 && coordination >= N * (M - 1)) {
            System.out.println(i);
            finished = true;

        }
    }

    private static void Number(int[] stones, int currentNumber, int previousNumber) {
        for (int j = 0; j < stones.length; j++) {
            if (stones[j] == previousNumber) {
                stones[j] = currentNumber;
                isFinished(stones[j], j);
            }
        }
    }

    private static void checkNeighbours(int[] stones, int coordination) {

        int arrayMin[] = new int[4];


        if (stones.length > coordination + 1 && (coordination + 1) % N != 0) {
            arrayMin[0] = stones[coordination + 1];
        }

        if(coordination -1 > -1) {
            if (coordination > 0 && (coordination % N != 0)) {
                arrayMin[1] = stones[coordination - 1];
            }
        }

        if(stones.length > coordination + N){
            arrayMin[2] = stones[coordination + N];
        }

        if(coordination - N > -1){
            arrayMin[3] = stones[coordination - N];
        }

        for (int j = 0; j < arrayMin.length; j++) {
            if(arrayMin[j] < stones[coordination] && arrayMin[j] != 0){
                Number(stones, arrayMin[j], stones[coordination]);
            }
        }

        for (int j = 0; j < arrayMin.length; j++) {
            if(arrayMin[j] > stones[coordination]){
                Number(stones, stones[coordination], arrayMin[j]);
            }
        }
    }


    private static void insert(int[] stones, int Ni, int Mi) {

        int coordination = Mi * N + Ni;

        if (coordination < N) {
            stones[coordination] = 1;
            checkNeighbours(stones, coordination);
        }else{
            stones[coordination] = p++;
            checkNeighbours(stones, coordination);
        }
    }
}