#include <bits/stdc++.h>
#define sz(x) ((int)x.size())
#define PB push_back
#define all(x) x.begin(),x.end()
using namespace std;
typedef long long ll;
const int N = 2010;
const int M = 30010;
const int PW = 10;
const int oo = 2e9;
const int md = 998244353;
vector<int> g[N];
queue<int> q;
int n, m, k, mrk[M], used[N], tt = 0, lf, rt;
ll ans = 0;
bool dfs(int v){
if (used[v] == tt) return 0;
used[v] = tt;
for (int u : g[v])
if (u >= lf && u <= rt && (mrk[u] < 0 || dfs(mrk[u]))){
mrk[u] = v;
return 1;
}
return 0;
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n >> m >> k;
for (int i = 0; i < k; i++){
int x, y;
cin >> x >> y;
x--; y--;
g[y].PB(x);
}
fill(mrk, mrk + n, -1);
for (int i = 0; i < m; i++)
q.push(i);
for (int l = 0, r = 0; l < n; l++){
while (r < n && sz(q)) {
lf = l; rt = r;
while (sz(q)) {
tt++;
int v = q.front();
if (dfs(v))
q.pop();
else break;
}
if (!sz(q)) break;
r++;
}
if (sz(q))
break;
ans += n - r;
if (mrk[l] >= 0){
q.push(mrk[l]);
mrk[l] = -1;
}
}
cout << ans;
return 0;
}
