1 #include <bits/stdc++.h>
  2 using namespace std;
  3 
  4 #define lrt rt << 1
  5 #define rrt rt << 1 | 1
  6 const int maxn = 5500;
  7 typedef struct Event {
  8     double l, r, hx;
  9     int sign;
 10 }Event;
 11 typedef struct Seg {
 12     double len;
 13     int sign;
 14 }Seg;
 15 
 16 vector<Event> event1, event2;
 17 double hx[maxn<<1], hy[maxn<<1];
 18 Seg seg[maxn<<2];
 19 int hxcnt, hycnt;
 20 int n;
 21 
 22 bool cmp(Event a, Event b) {
 23     if(a.hx != b.hx) return a.hx < b.hx;
 24     return a.sign > b.sign;
 25 }
 26 
 27 int xid(double x) {
 28     return lower_bound(hx, hx+hxcnt, x) - hx + 1;
 29 }
 30 
 31 int yid(double y) {
 32     return lower_bound(hy, hy+hycnt, y) - hy + 1;
 33 }
 34 
 35 void build(int l, int r, int rt) {
 36     seg[rt].len = .0; seg[rt].sign = 0;
 37     if(l == r) return;
 38     int mid = (l + r) >> 1;
 39     build(l, mid, lrt);
 40     build(mid+1, r, rrt);
 41 }
 42 
 43 void pushup(int l, int r, int rt) {
 44     if(seg[rt].sign) seg[rt].len = hx[r] - hx[l-1];
 45     else {
 46         if(l == r) seg[rt].len = .0;
 47         else seg[rt].len = seg[lrt].len + seg[rrt].len;
 48     }
 49 }
 50 
 51 void pushup1(int l, int r, int rt) {
 52     if(seg[rt].sign) seg[rt].len = hy[r] - hy[l-1];
 53     else {
 54         if(l == r) seg[rt].len = .0;
 55         else seg[rt].len = seg[lrt].len + seg[rrt].len;
 56     }
 57 }
 58 
 59 void update(bool flag, int L, int R, int sign, int l, int r, int rt) {
 60     if(L <= l && r <= R) {
 61         seg[rt].sign += sign;
 62         if(!flag) pushup(l, r, rt);
 63         else pushup1(l, r, rt);
 64         return;
 65     }
 66     int mid = (l + r) >> 1;
 67     if(L <= mid) update(flag, L, R, sign, l, mid, lrt);
 68     if(mid < R) update(flag, L, R, sign, mid+1, r, rrt);
 69     if(!flag) pushup(l, r, rt);
 70     else pushup1(l, r, rt);
 71 }
 72 
 73 int main() {
 74     // freopen("in", "r", stdin);
 75     int _ = 1;
 76     double ax, ay, bx, by;
 77     while(~scanf("%d",&n)) {
 78         hxcnt = 0; event1.clear(); event2.clear();
 79         for(int i = 0; i < n; i++) {
 80             scanf("%lf%lf%lf%lf",&ax,&ay,&bx,&by);
 81             event1.push_back({ax, bx, ay, 1});
 82             event1.push_back({ax, bx, by, -1});
 83             event2.push_back({ay, by, ax, 1});
 84             event2.push_back({ay, by, bx, -1});
 85             hx[hxcnt++] = ax; hx[hxcnt++] = bx;
 86             hy[hycnt++] = ay; hy[hycnt++] = by;
 87         }
 88         sort(event1.begin(), event1.end(), cmp);
 89         sort(event2.begin(), event2.end(), cmp);
 90         sort(hx, hx+hxcnt); hxcnt = unique(hx, hx+hxcnt) - hx;
 91         sort(hy, hy+hycnt); hycnt = unique(hy, hy+hycnt) - hy;
 92         build(1, hxcnt, 1);
 93         double ret = .0;
 94         double pre = .0;
 95         for(int i = 0; i < event1.size(); i++) {
 96             int l = xid(event1[i].l);
 97             int r = xid(event1[i].r) - 1;
 98             int sign = event1[i].sign;
 99             update(0, l, r, sign, 1, hxcnt, 1);
100             ret += abs(seg[1].len - pre);
101             pre = seg[1].len;
102         }
103         event1.clear();
104         build(1, hycnt, 1);
105         pre = .0;
106         for(int i = 0; i < event2.size(); i++) {
107             int l = yid(event2[i].l);
108             int r = yid(event2[i].r) - 1;
109             int sign = event2[i].sign;
110             update(1, l, r, sign, 1, hycnt, 1);
111             ret += abs(seg[1].len - pre);
112             pre = seg[1].len;
113         }
114         cout << ret << endl;
115     }
116     return 0;
117 }