package main

import (
	"fmt"
)

func main() {
	solve11()
}

func solve11(){
	var W, H, N int
	fmt.Scan(&W, &H, &N)
	var s, k int
	var ans int
	check := makeDoubleSliceInt(W, H)
	for i:=0; i<N; i++ {
	    fmt.Scan(&s, &k)
		s--
		k--
		if true{
			for i:=0; i<W; i++ {
			    if check[i][k]==0{
					check[i][k]=1
					ans++
				}
			}
			for j:=0; j<H; j++ {
			    if check[s][j]==0{
					check[s][j]=1
					ans++
				}
			}
		}
		ans--
	}
	fmt.Println(ans)
//	fmt.Println(check)
}

func makeDoubleSliceInt(y, x int) (ss [][]int) {
	ss = make([][]int, y)
	for i := range ss {
		ss[i] = make([]int, x)
	}
	return
}