#include <bits/stdc++.h>
#define lsb(x) (x & (-x))
#define ll long long
#define ull unsigned long long
#define ld long double
// 217
// 44
using namespace std;
const int MAXN = 30000;
struct MaxFlow {
const int INF = 1e9;
struct Edge {
int nod, id1, id2;
};
vector < vector <Edge> > g;
vector <Edge> from;
vector <int> cap, vis;
int n, m;
int sink, dest;
int now, ans;
inline void init(int _n, int _sink, int _dest) {
n = _n, sink = _sink, dest = _dest;
m = 0;
g.resize(n + 1);
from.resize(n + 1);
vis.resize(n + 1);
ans = now = 0;
}
inline void addEdge(int x, int y, int c) {
if(mp[{y, x}]) {
return ;
}
g[x].push_back({y, m, m + 1});
cap.push_back(c);
mp[{x, y}] = m;
g[y].push_back({x, m + 1, m});
cap.push_back(0);
mp[{y, x}] = m + 1;
m += 2;
}
inline bool bfs() {
queue <int> Q;
now++;
Q.push(sink);
vis[sink] = now;
while(Q.size()) {
int nod = Q.front();
Q.pop();
for(auto it : g[nod]) {
if(vis[it.nod] != now && cap[it.id1] > 0) {
Q.push(it.nod);
from[it.nod] = {nod, it.id1, it.id2};
vis[it.nod] = now;
}
}
}
return vis[dest] == now;
}
inline int flow() {
while(bfs()) {
int nod = dest;
int mn = INF;
while(nod != sink) {
mn = min(mn, cap[from[nod].id1]);
nod = from[nod].nod;
}
nod = dest;
while(nod != sink) {
cap[from[nod].id1] -= mn;
cap[from[nod].id2] += mn;
nod = from[nod].nod;
}
ans += mn;
}
return ans;
}
map < pair <int, int>, int > mp;
inline void delEdge(int x, int y) {
if(x > n) {
swap(x, y);
}
int id1 = mp[{x, y}];
int id2 = id1 + 1;
if(cap[id1] == 0) {
ans--;
cap[mp[{sink, x}]] = cap[mp[{y, dest}]] = 1;
}
cap[mp[{x, sink}]] = cap[mp[{dest, y}]] = 0;
cap[id1] = cap[id2] = 0;
}
};
vector <int> g[MAXN + 1];
int main() {
//ifstream cin("A.in");
//ofstream cout("A.out");
int i, n, m, k;
ios::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
cin >> n >> m >> k;
for(i = 1; i <= k; i++) {
int a, b;
cin >> a >> b;
g[a].push_back(b);
}
MaxFlow net;
net.init(n + m + 2, n + m + 1, n + m + 2);
for(i = 1; i <= n; i++) {
net.addEdge(net.sink, i, 1);
}
for(i = 1; i <= m; i++) {
net.addEdge(i + n, net.dest, 1);
}
int pos = 1;
ll ans = 0;
for(i = 1; i <= n; i++) {
bool ok = 0;
while(net.flow() < m && pos <= n) {
for(auto it : g[pos]) {
net.addEdge(pos, it + n, 1);
}
pos++;
ok = 1;
}
pos -= ok;
if(net.ans == m) {
ans += n - pos + 1;
}
for(auto it : g[i]) {
net.delEdge(i, it + n);
}
}
cout << ans;
//cin.close();
//cout.close();
return 0;
}
