#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(ll i=a;i<b;i++)
#define rrep(i,a,b) for(ll i=a-1;i>=b;i--)
#define ll long long
#define ull unsigned ll
#define ld long double
#define bl __int128_t
#define fi first
#define se second
#define vel vector<ll>
#define vvel vector<vel>
#define pll pair<ll,ll>
#define vepll vector<pll>
#define vvepll vector<vepll>
#define ves vector<string>
#define vem vector<mint>
#define vvem vector<vem>
#define pmm pair<mint,mint>
#define cleout(i) cout<<fixed<<setprecision(i)
template<class T>using PQ=priority_queue<T,vector<T>,greater<T>>;
//               上  右 下 左
vector<int> di={-1, 0, 1, 0};
vector<int> dj={ 0, 1, 0,-1};

vector<int> dx={ 0, 1, 0,-1};
vector<int> dy={ 1, 0,-1, 0};


vector<int> ddx={ 1, 1, 1, 0, -1, -1, -1, 0 };
vector<int> ddy={ 1, 0, -1, -1, -1, 0, 1, 1 };

ll inf=1000000000000000000;//1e18
// LLONG_MAX

void _solve(){
    ll H,W,N;
    cin>>H>>W>>N;
    vvel a(H+1,vel(W+1));
    rep(i,0,N){
        ll r1,c1,r2,c2;
        cin>>r1>>c1>>r2>>c2;
        r1--;
        c1--;
        a[r1][c1]++;
        a[r1][c2]--;
        a[r2][c1]--;
        a[r2][c2]++;
    }
    rep(i,0,H){
        rep(j,0,W){
            a[i][j+1]+=a[i][j];
        }
    }
    rep(j,0,W){
        rep(i,0,H){
            a[i+1][j]+=a[i][j];
        }
    }
    ll ans=0;
    rep(i,0,H){
        rep(j,0,W){
            if(a[i][j]==0)ans++;
        }
    }
    cout<<ans<<"\n";
}


int main(){
    cin.tie(nullptr);
 	ios_base::sync_with_stdio(false);

    
    ll _;
    bool multitest=0;
    if(multitest)cin>>_;
    else _=1;
    rep(__,0,_){
        _solve();
    }
}