1 // #pragma comment(linker, "/STACK:1024000000,1024000000")
2 #include <iostream>
3 #include <cstdio>
4 #include <cstring>
5 #include <sstream>
6 #include <string>
7 #include <algorithm>
8 #include <list>
9 #include <map>
10 #include <vector>
11 #include <queue>
12 #include <stack>
13 #include <cmath>
14 #include <cstdlib>
15 // #include <conio.h>
16 using namespace std;
17 #define clc(a,b) memset(a,b,sizeof(a))
18 #define inf 0x3f3f3f3f
19 #define lson l,mid,rt<<1
20 #define rson mid+1,r,rt<<1|1
21 const int N = 1100;
22 const int MOD = 1e9+7;
23 #define LL long long
24 #define mi() (l+r)>>1
25 double const pi = acos(-1);
26
27 // inline int r() {
28 // int x=0,f=1;char ch=getchar();
29 // while(ch>'9'||ch<'0') {if(ch=='-') f=-1;ch=getchar();}
30 // while(ch>='0'&&ch<='9') { x=x*10+ch-'0';ch=getchar();}return x*f;
31 // }
32 int n;
33 double hashh[N<<2];
34 double sum[N<<2];
35 int color[N<<2];
36 struct Edge{
37 double x1,x2,y;
38 int flag;
39 bool operator < (const Edge &a) const{
40 return y<a.y;
41 }
42 }e[N<<2];
43
44 int b_s(double x){
45 int l=1,r=2*n;
46 int mid;
47 while(l<=r){
48 mid=(l+r)>>1;
49 if(hashh[mid]==x) return mid;
50 else if(hashh[mid]<x) l=mid+1;
51 else r=mid-1;
52 }
53 }
54
55 void pushdown(int rt,int l,int r){
56 if(color[rt]) sum[rt]=hashh[r+1]-hashh[l];
57 else if(l==r) sum[rt]=0;
58 else sum[rt]=sum[rt<<1]+sum[rt<<1|1];
59 }
60
61 void update(int l,int r,int rt,int x,int y,int f){
62 if(x==l&&y==r){
63 color[rt]+=f;
64 pushdown(rt,l,r);
65 return;
66 }
67 int mid=mi();
68 if(y<=mid) update(l,mid,rt<<1,x,y,f);
69 else if(x>mid) update(mid+1,r,rt<<1|1,x,y,f);
70 else {
71 update(l,mid,rt<<1,x,mid,f);
72 update(mid+1,r,rt<<1|1,mid+1,y,f);
73 }
74 pushdown(rt,l,r);
75 }
76 int main(){
77 // int n;
78 while(scanf("%d",&n)){
79 if(n==0)
80 break;
81 clc(color,0);
82 clc(sum,0);
83 double x1,x2,y1,y2;
84 for(int i=1;i<=n;i++){
85 scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
86 e[i*2-1].x1=e[i*2].x1=x1;
87 e[i*2-1].x2=e[i*2].x2=x2;
88 e[i*2-1].y=y1;e[i*2].y=y2;
89 e[i*2-1].flag=1;e[i*2].flag=-1;
90 hashh[i*2-1]=x1;hashh[i*2]=x2;
91 }
92 sort(e+1,e+1+2*n);
93 sort(hashh+1,hashh+1+2*n);
94 double ans=0;
95 for(int i=1;i<=2*n;i++){
96 int l=b_s(e[i].x1),r=b_s(e[i].x2)-1;
97 // cout<<"l:"<<l<<" "<<"r:"<<r<<endl;
98 if(l<=r) update(1,2*n,1,l,r,e[i].flag);
99 // cout<<"sum[1]"<<sum[1]<<endl;
100 ans+=sum[1]*(e[i+1].y-e[i].y);
101 }
102 printf("%.2f\n",ans);
103 }
104 return 0;
105 }
