#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define fast ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
#define file(s) freopen(s".in", "r", stdin);freopen(s".out", "w", stdout);
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define pb push_back
#define sz size()
#define ft first
#define sd second
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef unsigned long long ull;
const int N = 2e5 + 10;
const int M = 1e3 + 5;
const ll inf = 2e18;
const ll mod = 1e9 + 7;
const double Pi = acos(-1);
ll binpow(ll x, ll ti) { ll res = 1;while (ti){if(ti & 1)res *= x;x *= x;ti >>= 1; x %= mod; res %= mod;} return res;}
ll binmul(ll x, ll ti) { ll res = 0;while (ti){if(ti & 1)res += x;x += x;ti >>= 1; x %= mod; res %= mod;} return res;}
ll nok(ll a, ll b) { return (a*b)/__gcd(abs(a),abs(b)) * (a*b > 0 ? 1 : -1); }
bool odd(ll n) { return (n % 2 == 1); }
bool even(ll n) { return (n % 2 == 0); }
ll n, m, k, a[N], b[N], mt[N], ans;
vector <ll> g[N];
bool used[N];
bool dfs(ll v, ll l, ll r) {
if (v < l || r < v) return 0;
used[v] = 1;
for (auto to : g[v]) {
if (mt[to] == -1) {
mt[to] = v;
return 1;
}
}
for (auto to : g[v]) {
if (!used[mt[to]] && dfs(mt[to], l, r)) {
mt[to] = v;
return 1;
}
}
return 0;
}
bool check(ll l, ll r) {
memset(mt, -1, sizeof(mt));
for (int i = l; i <= r; ++ i) {
memset(used, 0, sizeof(used));
dfs(i, l, r);
}
for (int i = 1; i <= m; ++ i) {
if (mt[i] == -1) return 0;
}
return 1;
}
const void solve(/*Armashka*/) {
cin >> n >> m >> k;
for (int i = 1; i <= k; ++ i) cin >> a[i] >> b[i], g[a[i]].pb(b[i]);
for (int i = 1; i <= n; ++ i) {
int l = 1, r = n - i + 1, j = -1;
while (l <= r) {
ll mid = (l + r) / 2;
if (check(i, i + mid - 1)) r = mid - 1, j = i + mid - 1;
else l = mid + 1;
}
if (j == -1) continue;
ans += n - j + 1;
}
cout << ans;
}
signed main() {
srand(time(NULL));
fast;
// file("");
int tt = 1;
// cin >> tt;
while (tt --) {
solve();
}
}
// Uaqyt, otedi, ketedi, mulde bilinbei, ulger
// Kunder seni kutpeidi, susyz ospeidi gulder
