using System;
using System.Linq;
using System.Collections.Generic;

class No11{
    static void Main(){
        var W = Int64.Parse(Console.ReadLine());
        var H = Int64.Parse(Console.ReadLine());
        var N = Int64.Parse(Console.ReadLine());
        var wHashSet = new HashSet<long>();
        var hHashSet = new HashSet<long>();
        for(int i=0;i<N;++i){
            var line=Console.ReadLine().Split(' ').Select(x=>Int64.Parse(x)).ToArray();
            wHashSet.Add(line[0]);
            hHashSet.Add(line[1]);
        }
        var c=(W-wHashSet.Count())*(H-hHashSet.Count());
        Console.WriteLine(W*H-c-N);
    }
}