using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

class Magatro
{
    
    static void Main()
    {
        long W = long.Parse(Console.ReadLine());
        long H = long.Parse(Console.ReadLine());
        long N = long.Parse(Console.ReadLine());
        HashSet<long> HashS = new HashSet<long>(),HashK=new HashSet<long>();
        for(int i = 0; i < N; i++)
        {
           long[] q = Console.ReadLine().Split(' ').Select(s=>long.Parse(s)).ToArray();
            HashS.Add(q[0]);
            HashK.Add(q[1]);
        }
        long All = W * H;
        long scnt = W - HashS.Count;
        long kcnt = H - HashK.Count;
        long cnt = scnt * kcnt + N;
        Console.WriteLine(All - cnt);
    }    

}