//看看会不会爆int!数组会不会少了一维！

//取物问题一定要小心先手胜利的条件

#include <bits/stdc++.h>

using namespace std;

#pragma comment(linker,"/STACK:102400000,102400000")

#define LL long long

#define ALL(a) a.begin(), a.end()

#define pb push_back

#define mk make_pair

#define fi first

#define se second

#define haha printf("haha\n")

const int maxn =  + ;

int n, m, k;

map<pair<int, int>, int> mp;

int color[maxn][maxn], h[maxn][maxn];

LL dp[maxn][maxn];

struct Point{

    int high, col;

};

int main(){

    scanf("%d%d%d", &n, &m, &k);

    for (int i = ; i <= k; i++){

        int a, b; scanf("%d%d", &a, &b);

        mp[mk(a, b)] = ;

        color[a][b] = ;

    }

    for (int i = ; i <= n; i++){

        for (int j = ; j <= m; j++){

            dp[i][j] = ;

            h[i][j] = ;

            if (color[i][j]) continue;

            h[i][j] = ;

            if (color[i][j] == color[i - ][j])

                h[i][j] += h[i - ][j];

        }

    }

    LL ans = ;

    for (int i = ; i <= n; i++){

        stack<Point> stc;

        for (int j = ; j <= m; j++){

            if (color[i][j] == ){

                while (!stc.empty()) stc.pop();

                continue;

            }

            int lb = j;

            while (!stc.empty()){

                if (stc.top().high >= h[i][j]) {

                    lb = stc.top().col; stc.pop();

                }

                else break;

            }

            dp[i][j] += 1LL * h[i][j] * (j - lb + );

            //printf("h[%d][%d] = %d lb = %d add = %lld\n", i, j, h[i][j], lb, 1LL*h[i][j] * (j - lb + 1));

            stc.push(Point{h[i][j], lb});

            if (color[i][lb - ] == ) dp[i][j] += dp[i][lb - ];

            ans += dp[i][j];

        }

    }

    cout << ans << endl;

    return ;

}