#include <iostream>
#include <vector>
#include <algorithm>
#include <cstring>
#include <cctype>
#include <string>
#include <queue>
#include <unordered_set>
#include <deque>
#include <numeric>
#include <cmath>
#include <unordered_map>
using namespace std;
#pragma GCC optimize("O3")
#pragma GCC optimization("Ofast,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
typedef long long ll;
int n, m, k;
vector<vector<int>> gr1, gr2;
vector<int> usedl, pairr;
vector<int> usedr, pairl;
bool kuhn_left(int v, int timer) {
usedl[v] = timer;
for (int u : gr1[v]) {
if (pairr[u] == -1 || (usedl[pairr[u]] != timer && kuhn_left(pairr[u], timer))) {
pairr[u] = v;
pairl[v] = u;
return true;
}
}
return false;
}
bool kuhn_right(int v, int timer, int min_allow, int max_allow) {
usedr[v] = timer;
for (int u : gr2[v]) {
if ((u >= min_allow && u <= max_allow) && (pairl[u] == -1 || (usedr[pairl[u]] != timer && kuhn_right(pairl[u], timer, min_allow, max_allow)))) {
pairl[u] = v;
pairr[v] = u;
return true;
}
}
return false;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cin >> n >> m >> k;
if (m > n) {
cout << 0 << '\n';
return 0;
}
gr1.resize(n);
gr2.resize(m);
for (int i = 0; i < k; ++i) {
int u, v;
cin >> u >> v;
u--, v--;
gr1[u].push_back(v);
gr2[v].push_back(u);
}
usedl.resize(n, -1);
usedr.resize(m, -1);
pairl.resize(n, -1);
pairr.resize(m, -1);
int timer = 0;
int cur_match = 0;
int max_allow = 0;
while (max_allow < n && cur_match < m) {
if (kuhn_left(max_allow++, timer++)) {
cur_match++;
}
}
if (cur_match < m) {
cout << 0 << '\n';
return 0;
}
ll ans = (n - max_allow + 1);
for (int i = 1; i < n; ++i) {
if (pairl[i - 1] != -1) {
int girl = pairl[i - 1];
pairr[girl] = -1;
pairl[i - 1] = -1;
cur_match--;
if (kuhn_right(girl, timer++, i, max_allow - 1)) {
cur_match++;
} else {
while (max_allow < n && cur_match < m) {
if (kuhn_left(max_allow++, timer++)) {
cur_match++;
}
}
}
}
if (cur_match != m) {
break;
}
ans += (n - max_allow + 1);
}
cout << ans << '\n';
}
