#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define dbg(x) cerr << #x << " " << x << "\n"
using ll = long long;
const int MAX_N = 3e4;
vector <int> gr[1 + MAX_N];
int pereche[1 + MAX_N];
int viz[1 + MAX_N];
int t;
int lb, rb;
bool bkt_op (int fata);
bool fits_req (int baiat) {
return lb <= baiat && baiat <= rb && (not pereche[baiat] || bkt_op (pereche[baiat]));
}
bool bkt_op (int fata) {
if (viz[fata] != t) {
viz[fata] = t;
for (int gagic : gr[fata]) {
if (fits_req (gagic)) {
pereche[gagic] = fata;
return true;
}
}
}
return false;
}
int main () {
ios::sync_with_stdio (false);
cin.tie (0); cout.tie (0);
int n, m, k;
cin >> n >> m >> k;
for (int i = 1; i <= k; i++) {
int x, y;
cin >> x >> y;
gr[y].pb (x);
}
for (int i = 1; i <= m; i++)
sort (gr[i].begin (), gr[i].end ());
lb = rb = 1;
ll ans = 0;
for (int i = 1; i <= m; i++) {
t++;
while(rb <= n && not bkt_op (i)) rb++, t++;
if (rb > n) {
cout << ans << "\n";
return 0;
}
}
vector <int> unpaired;
while (lb <= n) {
while (unpaired.size ()) {
int cur = unpaired.back ();
unpaired.pop_back ();
t++;
while(rb <= n && not bkt_op (cur)) rb++, t++;
if (rb > n) {
cout << ans << "\n";
return 0;
}
}
ans += (n - rb + 1);
if (pereche[lb]) {
unpaired.pb (pereche[lb]);
pereche[lb] = 0;
}
lb++;
}
cout << ans << "\n";
return 0;
}
