package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

var sc = bufio.NewScanner(os.Stdin)
var rdr = bufio.NewReaderSize(os.Stdin, 1000000)

func main() {
	sc.Split(bufio.ScanWords)
	w, h, n := nextInt64(), nextInt64(), nextInt64()
	ws := make(map[int]bool)
	hs := make(map[int]bool)
	for i := int64(0); i < n; i++ {
		ws[nextInt()] = true
		hs[nextInt()] = true
	}

	t := w*h - (w-int64(len(ws)))*(h-int64(len(hs))) - n
	fmt.Println(t)
}

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	i, _ := strconv.Atoi(nextLine())
	return i
}

func nextInt64() int64 {
	i, _ := strconv.ParseInt(nextLine(), 10, 64)
	return i
}