import java.util.*;
import java.io.*;
public class Main{
public static void main(String[] argv) throws IOException{
new Main().run();
}
int a[][] = new int [3891][3891];
int search(int x, int y){
	int k=0;
	if (a[x+1][y]==1)k++;
	if (a[x-1][y]==1)k++;
	if (a[x][y+1]==1)k++;
	if (a[x][y-1]==1)k++;
	return k;
}
PrintWriter pw;
Scanner sc;
public void run() throws IOException{
sc = new Scanner(new File("input.txt"));
pw = new PrintWriter(new File("output.txt"));

int n = sc.nextInt();
int x1[] = new int[n+1];
int y1[] = new int[n+1];
int x2[] = new int[n+1];
int y2[] = new int[n+1];
int maxx=-10000, maxy=-10000, minx=10000, miny=10000;

for(int k=1; k<=n; k++){
		x1[k]=sc.nextInt();
		y1[k]=sc.nextInt();
		x2[k]=sc.nextInt();
		y2[k]=sc.nextInt();
		
		if (x1[k]<minx)minx = x1[k];
		if (y1[k]<miny)miny = y1[k];
		if (x2[k]<minx)minx = x2[k];
		if (y2[k]<miny)miny = y2[k];
		if (x1[k]>maxx)maxx = x1[k];
		if (y1[k]>maxy)maxy = y1[k];
		if (x2[k]>maxx)maxx = x2[k];
		if (y2[k]>maxy)maxy = y2[k];
		}
int xz = -minx+1;
int yz = -miny+1;
minx = minx+xz;
miny = miny+yz;
maxx = maxx+xz;
maxy = maxy+yz;
for(int k=1; k<=n; k++){
	x1[k] = x1[k]+xz;
	x2[k] = x2[k]+xz;
	y1[k] = y1[k]+yz;
	y2[k] = y2[k]+yz;
	for(int i=x1[k]+1; i<=x2[k]; i++){
		for(int j=y1[k]+1; j<=y2[k]; j++){
			a[i][j]=1;
		}
	}
	}

int s = 0;
for(int i=minx; i<=maxx+2; i++){
	for(int j=miny; j<=maxy+2; j++){
		if (a[i][j]==0)s+=search(i, j);
		}
	}
pw.println(s);
pw.close();
}
}