#include <bits/stdc++.h>
#define DIM 30010
using namespace std;
vector <int> L[DIM];
bitset <DIM> f;
int Left[DIM],Right[DIM];
int n,m,k,i,x,y,cnt,st,dr;
int cupleaza (int nod){
if (f[nod])
return 0;
f[nod] = 1;
for (auto vecin : L[nod]){
if (!(vecin >= st && vecin <= dr))
continue;
if (!Right[vecin]){
Right[vecin] = nod;
Left[nod] = vecin;
cnt++;
return 1;
}
}
for (auto vecin : L[nod]){
if (!(vecin >= st && vecin <= dr))
continue;
if (cupleaza (Right[vecin])){
Left[nod] = vecin;
Right[vecin] = nod;
return 1;
}
}
return 0;
}
void cuplaj (){
int ok = 0;
do{
f.reset();
ok = 0;
for (int i=1;i<=n;i++){
if (!Left[i] && cupleaza (i))
ok = 1;
}
} while (ok);
}
int main (){
//ifstream cin ("date.in");
//ofstream cout ("date.out");
cin>>m>>n>>k;
for (i=1;i<=k;i++){
cin>>x>>y;
L[y].push_back(x);
}
int sol = 0;
st = 1;
for (dr=1;dr<=m;dr++){
if (dr >= n)
cuplaj();
while (cnt == n && st < dr){
if (Right[st]){
cnt--; /// ramane nodul din stanga necuplat
int nod = Right[st];
Left[nod] = Right[st] = 0;
}
st++;
cuplaj();
}
sol += st - 1;
}
cout<<sol;
return 0;
}
