/*
ID: xildar91
PROG: humble
LANG: C++11
*/
#include <bits/stdc++.h>
using namespace std;
typedef  long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<ll> vll;
int inf_int=2e9;
ll inf_ll=2e18;
typedef pair<int,int> pii;
#define pb push_back
const double pi=3.1415926535898;
#define dout if(debug) cout
#define fi first
#define se second
#define sp setprecision
#define sz size()

#define x1 gfgs
#define y1 asd
#define rank asdsad
bool debug=0;
const int maxn=1e5+7;

void solve()
{
    int n;
    cin >> n;
    ll x1[n],y1[n],x2[n],y2[n];;
    vector<pair<pair<ll,ll> ,ll> >a;
    for(int i=0;i<n;i++)
    {
        cin >> x1[i]>>y2[i]>>x2[i]>>y1[i];
        a.pb({{x1[i],0},i});
        a.pb({{x2[i],1},i});
    }
    sort(a.begin(),a.end());
    ll ans=0;
    set<pair<pii,int> > s;
    ll prev;
    for(int i=0;i<a.sz;i++)
    {
        if(!i)
        {
            int in=a[i].se;
            s.insert({{y1[in],y2[in]},in});
            prev=a[i].fi.fi;
        }
        else
        {
            ll dis=a[i].fi.fi-prev;
            ll mn=-inf_ll;
            for(auto x:s)
            {
                mn=max(mn,(ll)x.fi.fi);
                ll val=max((ll)0,(x.fi.se-mn)*dis);
                ans+=val;
                mn=max(mn,(ll)x.fi.se);

            }
            if(a[i].fi.se==1)
            {
                int in=a[i].se;
                s.erase({{y1[in],y2[in]},in});
            }
            else
            {
                int in=a[i].se;
                s.insert({{y1[in],y2[in]},in});
            }
            prev=a[i].fi.fi;
        }
    }
    cout << ans;



}






#define FILE "B-large"
int main()
{

     //   freopen("input.txt","r",stdin);
     //   freopen("output.txt","w",stdout);

        // freopen(FILE".in","r",stdin);
       // freopen(FILE".out","w",stdout);
       if(!debug)
       {
            ios_base::sync_with_stdio(0);
            cin.tie(0);
            cout.tie(0);
       }
        int t=1;
        while(t--)
            solve();
        return 0;
}