1 #include <cstdio>
  2 #include <cstring>
  3 #include <algorithm>
  4 #include <iostream>
  5 #include <vector>
  6 #include <queue>
  7 #include <cmath>
  8 #include <set>
  9 using namespace std;
 10 
 11 #define N 5005
 12 #define ll root<<1
 13 #define rr root<<1|1
 14 #define mid (a[root].l+a[root].r)/2
 15 
 16 int max(int x,int y){return x>y?x:y;}
 17 int min(int x,int y){return x<y?x:y;}
 18 int abs(int x,int y){return x<0?-x:x;}
 19 
 20 struct node{
 21     int l, r;
 22     int sum;
 23     int ysum;
 24     int val;
 25     bool lv, rv;
 26 }a[N*8];
 27 
 28 struct Line{
 29     int x1, x2, y;
 30     int val;
 31     Line(){}
 32     Line(int a,int b,int c,int d){
 33         x1=a;
 34         x2=b;
 35         y=c;
 36         val=d;
 37     }
 38 }line[N*2];
 39 
 40 bool cmp(Line a,Line b){
 41     return a.y<b.y;
 42 }
 43 int n, m;
 44 int xx[N*2];
 45 
 46 int b_s(int key){
 47     int l=1, r=m;
 48     while(l<=r){
 49         int mm=(l+r)/2;
 50         if(xx[mm]==key) return mm;
 51         else if(xx[mm]>key) r=mm-1;
 52         else if(xx[mm]<key) l=mm+1;
 53     }
 54 }
 55 
 56 void build(int l,int r,int root){
 57     a[root].l=l;
 58     a[root].r=r;
 59     a[root].ysum=a[root].sum=a[root].val=0;
 60     a[root].lv=a[root].rv=false;
 61     if(l==r) return;
 62     build(l,mid,ll);
 63     build(mid+1,r,rr);
 64 }
 65 
 66 void up(int root){
 67     if(a[root].val){
 68         a[root].sum=xx[a[root].r+1]-xx[a[root].l];
 69         a[root].lv=a[root].rv=true;
 70         a[root].ysum=2;    
 71     } 
 72     else if(a[root].l==a[root].r) {
 73         a[root].lv=a[root].rv=false;
 74         a[root].ysum=a[root].sum=0;
 75     }
 76     else{
 77         a[root].sum=a[ll].sum+a[rr].sum;
 78         a[root].lv=a[ll].lv;
 79         a[root].rv=a[rr].rv;
 80         a[root].ysum=a[ll].ysum+a[rr].ysum;
 81         if(a[rr].lv&&a[ll].rv) a[root].ysum-=2;
 82     } 
 83 }
 84 
 85 void update(int l,int r,int val,int root){
 86     if(a[root].l==l&&a[root].r==r){
 87         a[root].val+=val;
 88         up(root);
 89         return;
 90     }
 91     if(l>=a[rr].l) update(l,r,val,rr);
 92     else if(r<=a[ll].r) update(l,r,val,ll);
 93     else{
 94         update(l,mid,val,ll);
 95         update(mid+1,r,val,rr);
 96     }
 97     up(root);
 98 }
 99 
100 main()
101 {
102     int i, j, k;
103     int x1, y1, x2, y2;
104     int kase=1;
105     while(scanf("%d",&n)==1&&n){
106         m=1;k=0;
107         for(i=0;i<n;i++){
108             scanf("%d %d %d %d",&x1,&y1,&x2,&y2);
109             line[k++]=Line(x1,x2,y1,1);
110             line[k++]=Line(x1,x2,y2,-1);
111             xx[m++]=x1;xx[m++]=x2;
112         }
113         sort(xx+1,xx+m);
114         m=unique(xx+1,xx+m)-xx-1;
115         sort(line,line+k,cmp);
116         build(1,m,1);
117         int ans=0;
118         int pre=0;
119         for(i=0;i<k-1;i++){
120             update(b_s(line[i].x1),b_s(line[i].x2)-1,line[i].val,1);
121             ans+=abs(a[1].sum-pre)+(line[i+1].y-line[i].y)*a[1].ysum;
122             pre=a[1].sum;
123         }
124         update(b_s(line[k-1].x1),b_s(line[k-1].x2)-1,line[k-1].val,1);
125         ans+=abs(a[1].sum-pre);
126         printf("%d\n",ans);
127     }
128 }