using System;

namespace No011
{
  class Program
  {
    static void Main(string[] args)
    {
      long w, h, n, s, k;
      int sum = 0;
      char[,] card;

      w = int.Parse(Console.ReadLine());
      h = int.Parse(Console.ReadLine());
      n = int.Parse(Console.ReadLine());

      card = new char[w, h];

      for (int i = 0; i < n; i++)
      {
        string[] input = Console.ReadLine().Split(' ');
        s = int.Parse(input[0]) - 1;
        k = int.Parse(input[1]) - 1;
        for (int a = 0; a < w; a++)
        {
          for (int b = 0; b < h; b++)
          {
            if (a == s && b == k)
              card[a, b] = (char)2;
            else if (card[a, b] != 2)
            {
              if (a == s && b != k)
                card[a, b] = (char)1;
              else if (a != s && b == k)
                card[a, b] = (char)1;
            }
          }
        }
      }

      for (int a = 0; a < w; a++)
        for (int b = 0; b < h; b++)
          if (card[a, b] == 1)
            sum += (int)card[a, b];

      Console.WriteLine(sum);
    }
  }
}