/// In The Name Of God
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,sse3,sse4,popcnt,abm,mmx")
#include <bits/stdc++.h>
#define f first
#define s second
#define pb push_back
#define pp pop_back
#define mp make_pair
#define sz(x) (int)x.size()
#define sqr(x) ((x) * 1ll * (x))
#define all(x) x.begin(), x.end()
#define Kazakhstan ios_base :: sync_with_stdio(0), cin.tie(0), cout.tie(0);
#define nl '\n'
#define ioi exit(0);
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
const int N = (int)32000 + 7, inf = (int)1e9 + 7, mod = (int)1e9 + 7;
const ll linf = (ll)1e18 + 7;
const int dx[] = {-1, 0, 1, 0, 1, -1, -1, 1}, dy[] = {0, 1, 0, -1, 1, -1, 1, -1};
using namespace std;
int n, m, k;
vector <int> g[N];
int tmr, tmr1;
int p[N];
int was[N], good[N];
int dfs(int v, int L, int R) {
if (was[v] == tmr) return 0;
was[v] = tmr;
for (auto to : g[v]) {
if (!(L <= to && to <= R)) continue;
if (to > R) break;
if (p[to] == -1 || dfs(p[to], L, R)) {
p[to] = v;
return 1;
}
}
return 0;
}
int ok(int L, int R) {
L += m, R += m;
memset(p, -1, sizeof(p));
++tmr;
++tmr1;
int cnt = 0;
for (int i = 1; i <= m; i++) {
for (auto to : g[i]) {
if (p[to] == -1 && L <= to && to <= R) {
p[to] = i;
good[i] = tmr1;
++cnt;
break;
}
}
}
if (cnt == m) return 1;
for (int i = 1; i <= m; i++) {
if (good[i] == tmr1) continue;
++tmr;
cnt += dfs(i, L, R);
if (cnt == m) return 1;
}
return 0;
}
int main() {
#ifdef IOI2018
freopen ("in.txt", "r", stdin);
#endif
Kazakhstan
cin >> n >> m >> k;
for (int i = 1; i <= k; i++) {
int a, b;
cin >> b >> a;
g[a].pb(b + m);
}
int ans = 0;
for (int i = 1; i <= min(500, n); i++) {
int l = i, r = n, res = n + 1;
while (l <= r) {
int mid = l + r >> 1;
if (ok(i, mid)) res = mid, r = mid - 1;
else l = mid + 1;
}
ans += n - res + 1;
}
cout << ans;
ioi
}
