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#include <iostream>
#include <algorithm>
using namespace std;
#define LL long long
#define ULL unsigned long long
#define ls rt<<1
#define rs rt<<1|1
#define B1 131
#define B2 13331
#define M1 1000000007
#define M2 1000000009
#define eps 1e-8
#define MAXN 9e18
#define MS 5009
int n,m,k;
struct node{
int x1,y1;
int x2,y2;
}b[MS];
struct line{
int l,r,h,w;
}a[MS<<1];
int tot;
int tmp[MS<<1], num;
struct nod{
int val;
int mark;
}p[MS<<2];
bool cmp(line t1, line t2){
if(t1.h == t2.h) return t1.w > t2.w;
return t1.h < t2.h;
}
void init_x(){
num = tot = 0;
for(int i=1;i<=n;i++){
++num; tmp[num] = b[i].x1;
++num; tmp[num] = b[i].x2;
}
sort(tmp+1,tmp+num+1);
int len = num; num = 1;
for(int i=2;i<=len;i++){
if(tmp[i] != tmp[i-1]) tmp[++num] = tmp[i];
}
for(int i=1;i<=n;i++){
int l = lower_bound(tmp+1,tmp+num+1,b[i].x1) - tmp;
int r = lower_bound(tmp+1,tmp+num+1,b[i].x2) - tmp;
a[++tot] = {l,r,b[i].y1, 1};
a[++tot] = {l,r,b[i].y2,-1};
}
sort(a+1,a+tot+1,cmp);
}
void init_y(){
num = tot = 0;
for(int i=1;i<=n;i++){
++num; tmp[num] = b[i].y1;
++num; tmp[num] = b[i].y2;
}
sort(tmp+1,tmp+num+1);
int len = num; num = 1;
for(int i=2;i<=len;i++){
if(tmp[i] != tmp[i-1]) tmp[++num] = tmp[i];
}
for(int i=1;i<=n;i++){
int l = lower_bound(tmp+1,tmp+num+1,b[i].y1) - tmp;
int r = lower_bound(tmp+1,tmp+num+1,b[i].y2) - tmp;
a[++tot] = {l,r,b[i].x1, 1};
a[++tot] = {l,r,b[i].x2,-1};
}
sort(a+1,a+tot+1,cmp);
}
void build(int l,int r,int rt){
p[rt] = {0,0};
if(l == r) return;
int m = l+r>>1;
build(l,m,ls);
build(m+1,r,rs);
}
void push_up(int rt,int l,int r){
if(p[rt].mark) p[rt].val = tmp[r+1] - tmp[l];
else if(l == r) p[rt].val = 0;
else p[rt].val = p[ls].val + p[rs].val;
}
void modify(int L,int R,int l,int r,int rt,int val){
if(L <= l && r <= R){
p[rt].mark += val;
push_up(rt,l,r);
return;
}
int m = l+r>>1;
if(m >= L) modify(L,R,l,m,ls,val);
if(m < R) modify(L,R,m+1,r,rs,val);
push_up(rt,l,r);
}
int cal(){
int ans = 0;
build(1,num-1,1);
for(int i=1;i<=tot;i++){
int t = p[1].val;
modify(a[i].l,a[i].r-1,1,num-1,1,a[i].w);
ans += (int)abs(p[1].val - t);
}
return ans;
}
void solve(){
for(int i=1;i<=n;i++){
int x1,y1,x2,y2; cin >> x1 >> y1 >> x2 >> y2;
b[i] = {x1,y1,x2,y2};
}
int ans = 0;
init_x(); ans += cal();
init_y(); ans += cal();
cout << ans << "\n";
}
int main(){
ios::sync_with_stdio(false);
int ce = 1;
while(cin >> n){
solve();
}
}
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