#include <iostream>
#include <queue>
#include <vector>
#include "main.h"

using namespace std;

struct apple {
    int row, col;
    bool isRotten;

    apple(int _row, int _col, bool _isRotten) {
        row = _row;
        col = _col;
        isRotten = _isRotten;
    }

    apple() {
        row = 0;
        col = 0;
        isRotten = false;
    }
};

bool isOutOfBounds(apple a, int rows, int cols) {
    if (a.row < 0 || a.row >= rows || a.col < 0 || a.col >= cols) {
        return true;
    }
    return false;
}

int main() {
    int rottenCount = 0;
    int rows, cols, days;
    cin >> rows >> cols >> days;
    queue<apple> rotten = queue<apple>();
    vector<vector<apple>> apples = vector<vector<apple>>();
    for (int i = 0; i < rows; i++) {
        vector<apple> row = vector<apple>();
        for (int j = 0; j < cols; j++) {
            row.push_back(apple(i, j, false));
        }
        apples.push_back(row);
    }
    int rottenX, rottenY;
    while (cin >> rottenX >> rottenY) {
        apples[rottenX - 1][rottenY - 1].isRotten = true;
        rotten.push(apple(rottenX - 1, rottenY - 1, true));
        rottenCount++;
    }

    for (int i = 0; i < days; i++) {
        int size = rotten.size();
        for (int j = 0; j < size; j++) {
            apple curr = rotten.front();
            //add left (from current) apple to rotten
            apple left = apple(curr.row, curr.col - 1, true);
            if (!isOutOfBounds(left, rows, cols) && !apples[curr.row][curr.col - 1].isRotten) {
                rottenCount++;
                apples[curr.row][curr.col - 1].isRotten = true;
                rotten.push(left);
            }
            //add right (from current) apple to rotten
            apple right = apple(curr.row, curr.col + 1, true);
            if (!isOutOfBounds(right, rows, cols) && !apples[curr.row][curr.col + 1].isRotten) {
                rottenCount++;
                apples[curr.row][curr.col + 1].isRotten = true;
                rotten.push(right);
            }
            //add down (from current) apple to rotten
            apple down = apple(curr.row + 1, curr.col, true);
            if (!isOutOfBounds(down, rows, cols) && !apples[curr.row + 1][curr.col].isRotten) {
                rottenCount++;
                apples[curr.row + 1][curr.col].isRotten = true;
                rotten.push(down);
            }
            //add up (from current) apple to rotten
            apple up = apple(curr.row - 1, curr.col, true);
            if (!isOutOfBounds(up, rows, cols) && !apples[curr.row - 1][curr.col].isRotten) {
                rottenCount++;
                apples[curr.row - 1][curr.col].isRotten = true;
                rotten.push(up);
            }
            rotten.pop();
        }
    }

    cout << rows * cols - rottenCount;
    return 0;
}