#include<stdio.h>

#include<stdlib.h>

#include<cstring>

#include<math.h>

#include<algorithm>

#include<vector>

using namespace std;

const int maxn=100005;

struct Rectangle

{

 int x1,y1,x2,y2;

};

struct Event

{

 int x,y1,y2,add;

};

struct IntervalTreeNode

{

 int count,total;

};

int n;

Rectangle rect[maxn];

Event evt[maxn<<1];

IntervalTreeNode tree[(maxn+10)<<2];

int id[maxn<<1];

bool cmp(const Event &a,const Event &b)

{

 if(a.x<b.x)return true;

 	return false;

}

void up(int i,int lb,int rb)

{

 tree[i].total=tree[i<<1].total+tree[(i<<1)+1].total;

 if(tree[i].count)tree[i].total=id[rb]-id[lb];

}

void ins(int i,int lb,int rb,int a,int b,int k)

{

 if(a==lb&&b==rb){

 	tree[i].count+=k;

 	up(i,lb,rb);

 	return ;

 }

 int med=(lb+rb)>>1;

 if(b<=med) ins(i<<1,lb,med,a,b,k);

 	else if(a>=med)ins((i<<1)+1,med,rb,a,b,k);

 		else{

 			 ins(i<<1,lb,med,a,med,k);

 			 ins((i<<1)+1,med,rb,med,b,k);

		 }

 up(i,lb,rb);

}

long long area()

{

 for(int i=0;i<n;i++){

 	id[i]=rect[i].y1;

 	id[i+n]=rect[i].y2;

 }

 sort(id,id+2*n);

 for(int i=0;i<2*n;i++){

 	rect[i].y1=lower_bound(id,id+2*n,rect[i].y1)-id;

 	rect[i].y2=lower_bound(id,id+2*n,rect[i].y2)-id;//坐标离散化

 }

 for(int i=0;i<n;i++){

 	evt[i].add=1;

 	evt[i+n].add=-1;

 	evt[i].x=rect[i].x1;

 	evt[i+n].x=rect[i].x2;

 	evt[i].y1=evt[i+n].y1=rect[i].y1;

 	evt[i].y2=evt[i+n].y2=rect[i].y2;

 }

 sort(evt,evt+n*2,cmp);

 long long int ans=0;

 for(int i=0;i<2*n;i++){

 	if(i>0&&evt[i].x>evt[i-1].x){

 		ans+=(long long )(evt[i].x-evt[i-1].x)*tree[1].total;

	 }

	ins(1,0,2*n-1,evt[i].y1,evt[i].y2,evt[i].add);

 }

 return ans;

}

int main()

{freopen("t.txt","r",stdin);

 while(true)

 {

 	n=0;

 	scanf("%d%d%d%d",&rect[0].x1,&rect[0].y1,&rect[0].x2,&rect[0].y2);

 	if(rect[0].x1==-1)return -1;

 	while(++n)

 		{

 		 scanf("%d%d%d%d",&rect[n].x1,&rect[n].y1,&rect[n].x2,&rect[n].y2);

 		 if(rect[n].x1==-1)break;

		}

	printf("%I64d\n",area());

 }

 return 0;

}