#include <iostream>
#include <algorithm>
#include <string.h>
#define ls (rt<<1)
#define rs (rt<<1|1)
using namespace std;
const int maxn = 40005;

int cover[maxn];
double length[maxn];
double yy[maxn];

struct ScanLine
{
	double x;
	double upy,downy;
	int inout;
	ScanLine(){}
	ScanLine(double x,double y1,double y2,int io):x(x),upy(y1),downy(y2),inout(io){}
}line[maxn];
bool cmp(ScanLine &a,ScanLine &b)
{
	return a.x<b.x;
}
void pushup(int l,int r,int rt)
{
	if(cover[rt]) length[rt] = yy[r]-yy[l];
	else if(l+1==r) length[rt] = 0;
	else length[rt] = length[ls]+length[rs];
}
void update(int yl,int yr,int io,int l,int r,int rt)
{
	if(yl>r||yr<l) return ;
	if(yl<=l&&yr>=r)
	{
		cover[rt] += io;
		pushup(l,r,rt);
		return ;
	}
	if(l+1==r)return ;
	int m = (l+r)>>1;
	if(yl<=m)
		update(yl,yr,io,l,m,ls);
	if(yr>m)
		update(yl,yr,io,m,r,rs);
	pushup(l,r,rt);
}

int main()
{
	int n;
	cin>>n;
	int cnt = 0;
	double x1,x2,y1,y2;
	int yr,yl;
	int io;
	for(int i=1;i<=n;i++)
	{	
		scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
		line[++cnt] = ScanLine(x1,y2,y1,1);
		yy[cnt] = y1;
		line[++cnt] = ScanLine(x2,y2,y1,-1);
		yy[cnt] = y2;
	}	
	sort(yy+1,yy+cnt+1);
	sort(line+1,line+cnt+1,cmp);
	int len = unique(yy+1,yy+cnt+1)-(yy+1);
	memset(cover,0,sizeof(cover));
	memset(length,0,sizeof(length));
	double ans = 0;
	for(int i = 1;i<=cnt;i++)
	{	
		ans += length[1]*(line[i].x-line[i-1].x);
		yl = lower_bound(yy+1,yy+len+1,line[i].downy)-yy;
		yr = lower_bound(yy+1,yy+len+1,line[i].upy)-yy;
		io=line[i].inout;
		update(yl,yr,io,1,len,1);
	}	
	cout<<ans;
	return 0;
}

hack数据

in:
2
0 5 4 1
2 4 6 2
答案out:
20
程序输出：
0