#include<bits/stdc++.h>
#define IOS ios_base::sync_with_stdio(false);cin.tie();cout.tie();
#define all(x) x.begin(), x.end()
#define int long long
#define pq priority_queue
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define pp pop_back
#define F first
#define S second
using namespace std;
int L, R, T;
int mt[30005];
int vis[2005];
queue<int> q;
vector<int> adj[2005];
bool dfs(int s) {
if (vis[s] == T) return 0;
vis[s] = T;
for (int i: adj[s]) {
if (L > i || i > R) continue;
if (!mt[i] || dfs(mt[i])) {mt[i] = s; return 1;}
}
return 0;
}
bool check() {
while(!q.empty()) {
int s = q.front(); q.pop();
T++;
if (!dfs(s)) {
q.push(s);
return 0;
}
}
return 1;
}
void solve () {
int N, M, Q; cin >> N >> M >> Q;
while (Q--) {int x, y; cin >> x >> y; adj[y].pb(x);}
for (int i = 1; i <= M; i++) q.push(i);
int ans = 0; R = 1;
for (L = 1; L <= N; L++) {
while (R <= N && !check()) R++;
ans += N - R + 1;
if (mt[L]) {
q.push(mt[L]);
mt[L] = 0;
}
}
cout << ans;
}
signed main() {IOS solve(); return 0;}
