#include <bits/stdc++.h>
#define sz(x) ((int)x.size())
#define PB push_back
#define MP make_pair
#define y first
#define psh second
#define edge pair<int, int>
#define pi3 pair<pii, int>
#define MP3(a,b,c) MP(MP(a, b), c)
using namespace std;
const int oo = 1e9;
const int N = 32100;
const int K = 110;
const int PW = 20;
vector<edge> edges;
queue<int> q;
vector<int> g[N];
int ans = 0, s, t, n, m, k, dst[N], ptr[N];
void add_edge(int x, int y){
g[x].PB(sz(edges));
edges.PB(edge(y, 0));
g[y].PB(sz(edges));
edges.PB(edge(x, 1));
}
bool bad(int l, int r, int v){
if (v == s || v == t || v < m) return 0;
return !(m + l <= v && v <= m + r);
}
bool bfs(int l, int r){
fill(dst, dst + t + 1, oo);
dst[s] = 0;
while (sz(q)) q.pop();
q.push(s);
while (sz(q)){
int v = q.front(); q.pop();
for (int nm : g[v]){
edge u = edges[nm];
if (!bad(l, r, u.y) && !u.psh && dst[u.y] > dst[v] + 1){
dst[u.y] = dst[v] + 1;
q.push(u.y);
}
}
}
return (dst[t] < oo);
}
bool dfs(int v, bool pshd){
if (pshd == 0) return 0;
if (v == t) return pshd;
for (; ptr[v] < sz(g[v]); ptr[v]++){
int nm = g[v][ptr[v]];
edge u = edges[nm];
if (dst[u.y] != dst[v] + 1) continue;
int nw = dfs(u.y, min(pshd, !u.psh));
if (nw){
edges[nm].psh = 1;
edges[nm ^ 1].psh = 0;
return nw;
}
}
return 0;
}
bool ok(int l, int r){
if (r - l + 1 < m) return 0;
int flow = 0;
for (int i = 0; i < m; i++) {
int nm = g[s][i];
flow += edges[nm].psh;
}
while (bfs(l, r)){
fill(ptr, ptr + t + 1, 0);
int pshd = dfs(s, oo);
while (pshd > 0){
flow += pshd;
pshd = dfs(s, oo);
}
}
return (flow == m);
}
int main(){
ios_base::sync_with_stdio(0); cin.tie(0);
cin >> n >> m >> k;
for (int i = 0; i < k; i++){
int x, y; cin >> y >> x;
x--; y--;
add_edge(x, m + y);
}
s = n + m;
t = n + m + 1;
for (int i = 0; i < m; i++)
add_edge(s, i);
for (int i = 0; i < n; i++)
add_edge(i + m, t);
for (int l = 0, r = 0; l < n; l++){
if (l + m - 1 >= n) break;
while (r < n && !ok(l, r))
r++;
if (r >= n) break;
ans += n - r;
int nm = g[t][l];
if (edges[nm].psh) continue;
int pr = -1, cr = m + l;
for (int it = 0; it < sz(g[cr]); it++){
int nm = g[cr][it];
edge ed = edges[nm];
if (ed.y != t && !ed.psh){
pr = ed.y;
break;
}
}
nm = g[s][pr];
edges[nm].psh = 0;
edges[nm ^ 1].psh = 1;
}
cout << ans;
return 0;
}
