#include <iostream>
#include <queue>
using namespace std;
struct Point {
	int row, column;
	Point* top;
	Point* bottom;
	Point* left;
	Point* right;
	Point(int row, int column){
		this->row = row;
		this->column = column;
		top = nullptr;
		bottom = nullptr;
		left = nullptr;
		right = nullptr;
	}
};
void printTable(int** definiteArray, int rows, int columns) {
	for (int i = rows; i >= 1; i--) {
		for (int j = 1; j <= columns ; j++) {
			cout << definiteArray[i][j] << " ";
		}
		cout << endl;
	}
	cout << endl << endl;
}
void fulfillTable(int** definiteArray, int rows, int columns) {
	for (int i = 1; i <= rows; i++) {
		for (int j = 1; j <= columns; j++) {
			definiteArray[i][j] = 0;
		}
	}
}
int main() {
	int rows, columns;
	int numberOfDays;
	cin >> rows >> columns >> numberOfDays;
	int** table = new int*[rows + 1];
	for (int i = 0; i <= rows + 1; i++) {
		table[i] = new int[columns + 1];
	}
	fulfillTable(table, rows, columns);
	int counterOfRottenApples = 0;
	queue<Point> currentRotten;
	int row, column;
	while(cin >> row >> column){
		Point* current = new Point(row, column);
		currentRotten.push(*current);
		table[row][column] = 1;
		counterOfRottenApples++;
	}
	//printTable(table, rows, columns);
	queue<Point> temporary;
	for (int i = 0; i < numberOfDays; i++) {
		while (!currentRotten.empty()) {
			int temporaryRow = currentRotten.front().row;
			int temporaryColumn = currentRotten.front().column;
			if (table[temporaryRow - 1][temporaryColumn] != 1
				&& temporaryRow - 1 >= 1){

				counterOfRottenApples++;
				table[temporaryRow - 1][temporaryColumn] = 1;
				Point* pointToAdd = new Point(temporaryRow - 1, temporaryColumn);
				temporary.push(*pointToAdd);
			}
			if (temporaryRow + 1 <= rows
				&& table[temporaryRow + 1][temporaryColumn] != 1) {

				table[temporaryRow + 1][temporaryColumn] = 1;
				counterOfRottenApples++;
				Point* pointToAdd = new Point(temporaryRow + 1, temporaryColumn);
				temporary.push(*pointToAdd);
			}
			if (temporaryColumn - 1 >= 1 && table[temporaryRow][temporaryColumn - 1] != 1) {

				counterOfRottenApples++;
				table[temporaryRow][temporaryColumn - 1] = 1;
				Point* pointToAdd = new Point(temporaryRow, temporaryColumn - 1);
				temporary.push(*pointToAdd);
			}
			if (temporaryColumn + 1 <= columns && table[temporaryRow][temporaryColumn + 1] != 1) {

				counterOfRottenApples++;
				table[temporaryRow][temporaryColumn + 1] = 1;
				Point* pointToAdd = new Point(temporaryRow, temporaryColumn + 1);
				temporary.push(*pointToAdd);
			}
			currentRotten.pop();
			//printTable(table, rows, columns);
		}
		while (!temporary.empty()) {
			currentRotten.push(temporary.front());
			temporary.pop();
		}
		//printTable(table, rows, columns);
	}
	cout << (rows * columns) - counterOfRottenApples;
}