#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<int, int> Pi;
typedef vector<ll> Vec;
typedef vector<int> Vi;
typedef vector<string> Vs;
typedef vector<P> VP;
typedef vector<vector<ll>> VV;
typedef vector<vector<int>> VVi;

#define REP(i, a, b) for(ll i=(a); i<(b); i++)
#define PER(i, a, b) for(ll i=(a); i>=(b); i--)
#define rep(i, n) REP(i, 0, n)
#define per(i, n) PER(i, n, 0)
const ll INF=1e18+18;
const ll MAX=100005;
const ll MOD=1000000007;
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl;
#define YES(n) cout << ((n) ? "YES" : "NO") << endl;
#define ALL(v) v.begin(), v.end()
#define rALL(v) v.rbegin(), v.rend()
#define pb(x) push_back(x)
#define mp(a, b) make_pair(a,b)
#define Each(a,b) for(auto &a :b)
#define REPM(i, mp) for (auto i = mp.begin(); i != mp.end(); ++i)
#define dbg(x_) cerr << #x_ << ":" << x_ << endl;
#define dbgmap(mp) cerr << #mp << ":"<<endl; for (auto i = mp.begin(); i != mp.end(); ++i) { cerr << i->first <<":"<<i->second << endl;}
#define dbgarr(n,m,arr) rep(i,n){rep(j,m){cerr<<arr[i][j]<<" ";}cerr<<endl;}
#define dbgdp(n,arr) rep(i,n){cerr<<arr[i]<<" ";}cerr<<endl;
#define dbgmint(n,arr) rep(i,n){cerr<<arr[i].x<<" ";}cerr<<endl;
#define out(a) cout<<a<<endl
#define out2(a,b) cout<<a<<" "<<b<<endl
#define vout(v) rep(i,v.size()){cout<<v[i]<<" ";}cout<<endl
#define Uniq(v) v.erase(unique(v.begin(), v.end()), v.end())
#define fi first
#define se second

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }

template<typename T1, typename T2>
ostream &operator<<(ostream &s, const pair<T1, T2> &p) { return s<<"("<<p.first<<", "<<p.second<<")"; }

template<typename T>istream& operator>>(istream&i,vector<T>&v)
{rep(j,v.size())i>>v[j];return i;}

// vector
template<typename T>
ostream &operator<<(ostream &s, const vector<T> &v) {
    int len=v.size();
    for(int i=0; i<len; ++i) {
        s<<v[i];
        if(i<len-1) s<<"	";
    }
    return s;
}

// 2 dimentional vector
template<typename T>
ostream &operator<<(ostream &s, const vector<vector<T> > &vv) {
    int len=vv.size();
    for(int i=0; i<len; ++i) {
        s<<vv[i]<<endl;
    }
    return s;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout<<std::setprecision(10);

    ll n;
    cin>>n;
    Vec x1(n);
    Vec x2(n);
    Vec y1(n);
    Vec y2(n);
    Vec cx;
    Vec cy;
    rep(i,n){
        cin>>x1[i]>>y1[i]>>x2[i]>>y2[i];
        cx.pb(x1[i]);
        cx.pb(x2[i]);
        cy.pb(y1[i]);
        cy.pb(y2[i]);
    }
    sort(ALL(cx));
    sort(ALL(cy));
    Uniq(cx);
    Uniq(cy);
    ll N = 2*n;
    VV dp(N,Vec(N));

    rep(i,n){
        ll px1 = lower_bound(ALL(cx),x1[i])-cx.begin();
        ll px2 = lower_bound(ALL(cx),x2[i])-cx.begin();
        ll py1 = lower_bound(ALL(cy),y1[i])-cy.begin();
        ll py2 = lower_bound(ALL(cy),y2[i])-cy.begin();
        dp[px1][py1]++;
        dp[px2][py1]--;
        dp[px1][py2]--;
        dp[px2][py2]++;
    }
    //dbg(dp);

    REP(i,1,N){
        rep(j,N){
            dp[i][j]+=dp[i-1][j];
        }
    }
    rep(i,N){
        REP(j,1,N){
            dp[i][j]+=dp[i][j-1];
        }
    }

    ll ans=0;
    rep(i,N-1){
        rep(j,N-1){
            if(dp[i][j]>=1){
                ans += (cx[i+1]-cx[i])*(cy[j+1]-cy[j]);
            }
        }
    }
    cout<<ans<<endl;
    return  0;
}



Measured memory_bytes: 128192