#include <bits/stdc++.h>
using namespace std;
#define forn(i, a, b) for(int i=a; i<=b; ++i)
const int maxN = 3e4 +10;
const int maxM = 2e3 +10;
int matched[maxN];
vector<int> E[maxM];
int le, ri, t = 1;
int N, M, K;
long long result;
int visited[maxM];
vector<int> not_match;
bool visit(int u) {
if (visited[u] == t) return false;
visited[u] = t;
while (E[u].size() && E[u].back() < le) E[u].pop_back();
for(auto v: E[u]) if (le <= v && v <= ri) {
if (!matched[v] || visit(matched[v])) {
matched[v] = u;
return true;
}
}
return false;
}
int main() {
ios::sync_with_stdio(0);
cin >> N >> M >> K;
forn(i, 1, K) {
int Ai, Bi;
cin >> Ai >> Bi;
E[Bi].push_back(Ai);
}
forn(i, 1, M) {
sort(E[i].begin(), E[i].end());
reverse(E[i].begin(), E[i].end());
}
forn(i, 1, M) not_match.push_back(i);
for(le = 1; le <= N; ++le) {
if (le > 1 && matched[le-1]) {
not_match.push_back(matched[le-1]);
matched[le-1] = 0;
}
while (ri < N && not_match.size()) {
ri ++;
t ++;
if (visit(not_match.back())) not_match.pop_back();
}
if (not_match.empty()) result += N-ri+1;
}
cout << result;
}
