#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<cstdio>
#include<sstream>
#include<iomanip>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mp make_pair
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)
using namespace std;
//kaewasuretyuui
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef pair<int,pii> pip;
typedef vector<pip>vip;
const double PI=acos(-1);
const double EPS=1e-8;
const int inf=1e8;
int main(){
	int n;
	cin>>n;
	vvi in(n,vi(4));
	rep(i,n)rep(j,4)cin>>in[i][j];
	vi x,y;
	rep(i,n)rep(j,4)if(j%2)y.pb(in[i][j]);
					else x.pb(in[i][j]);
	sort(all(x));sort(all(y));
	x.erase(unique(all(x)),x.end());
	y.erase(unique(all(y)),y.end());
	
	vvi tmp=in;
	rep(i,n)rep(j,4)if(j%2)tmp[i][j]=lower_bound(all(y),tmp[i][j])-y.begin();
					else tmp[i][j]=lower_bound(all(x),tmp[i][j])-x.begin();
	vvi field(x.size(),vi(y.size()));

	rep(i,n){
		field[tmp[i][0]][tmp[i][1]]++;
		field[tmp[i][2]][tmp[i][1]]--;
		field[tmp[i][0]][tmp[i][3]]--;
		field[tmp[i][2]][tmp[i][3]]++;
	}
	rep(i,x.size())loop(j,1,y.size())field[i][j]+=field[i][j-1];
	rep(j,y.size())loop(i,1,x.size())field[i][j]+=field[i-1][j];
	
	//loop(j,tmp[i][0],tmp[i][2])loop(k,tmp[i][1],tmp[i][3])

	ll out=0;
	rep(i,x.size())rep(j,y.size())if(field[i][j])
		out+=(ll)(x[i+1]-x[i])*(y[j+1]-y[j]);
	cout<<out<<endl;
}