#include <cstdio>
#include <algorithm>
#define LEN 10000
using namespace std;
struct Node
{
int left;
int right;
int count;//被覆盖次数
int line;//所包含的区间数量
int lbd;//左端点是否被覆盖
int rbd;//右端点是否被覆盖
int m;//测度
};
struct ScanLine
{
int x;
int y1;
int y2;
int flag;
};
struct Node node[LEN*4];
struct ScanLine scan[LEN];
int y[LEN];
void build(int l, int r, int i)
{
node[i].left = l;
node[i].right = r;
node[i].count = 0;
node[i].m = 0;
node[i].line = 0;
if (r - l > 1)
{
int middle = (l + r)/2;
build(l, middle, 2*i + 1);
build(middle, r, 2*i + 2);
}
}
//更新测度m
void update_m(int i)
{
if (node[i].count > 0)
node[i].m = y[node[i].right] - y[node[i].left];
else if (node[i].right - node[i].left == 1)
node[i].m = 0;
else
{
node[i].m = node[2*i + 1].m + node[2*i + 2].m;
}
}
//更新line
void update_line(int i)
{
if (node[i].count > 0)
{
node[i].lbd = 1;
node[i].rbd = 1;
node[i].line = 1;
}
else if (node[i].right - node[i].left == 1)
{
node[i].lbd = 0;
node[i].rbd = 0;
node[i].line = 0;
}
else
{
node[i].lbd = node[2*i + 1].lbd;
node[i].rbd = node[2*i + 2].rbd;
node[i].line = node[2*i + 1].line + node[2*i + 2].line - node[2*i + 1].rbd*node[2*i + 2].lbd;
}
}
void insert(int l, int r, int i)
{
//在这里要取离散化之前的原值进行比较
if (y[node[i].left] >= l && y[node[i].right] <= r)
(node[i].count)++;
else if (node[i].right - node[i].left == 1)
return;
else
{
int middle = (node[i].left + node[i].right)/2;
if (r <= y[middle])
insert(l, r, 2*i + 1);
else if (l >= y[middle])
insert(l, r, 2*i + 2);
else
{
insert(l, y[middle], 2*i + 1);
insert(y[middle], r, 2*i + 2);
}
}
update_m(i);
update_line(i);
}
void remove(int l, int r, int i)
{
在这里要取离散化之前的原值进行比较
if (y[node[i].left] >= l && y[node[i].right] <= r)
(node[i].count)--;
else if (node[i].right - node[i].left == 1)
return;
else
{
int middle = (node[i].left + node[i].right)/2;
if (r <= y[middle])
remove(l, r, 2*i + 1);
else if (l >= y[middle])
remove(l, r, 2*i + 2);
else
{
remove(l, y[middle], 2*i + 1);
remove(y[middle], r, 2*i + 2);
}
}
update_m(i);
update_line(i);
}
bool cmp(struct ScanLine line1, struct ScanLine line2)
{
if (line1.x == line2.x)
return line1.flag > line2.flag;
return (line1.x < line2.x);
}
int main()
{
int n;
scanf("%d", &n);
int x1, y1, x2, y2;
int i = 0;
while (n--)
{
scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
scan[i].x = x1;
scan[i].y1 = y1;
scan[i].y2 = y2;
scan[i].flag = 1;
y[i++] = y1;
scan[i].x = x2;
scan[i].y1 = y1;
scan[i].y2 = y2;
scan[i].flag = 0;
y[i++] = y2;
}
sort(y, y + i);
sort(scan, scan + i, cmp);
//y数组中不重复的个数
int unique_count = unique(y, y + i) - y;
//离散化,建立线段树
build(0, unique_count - 1, 0);
int perimeter = 0;
int now_m = 0;
int now_line = 0;
for (int j = 0; j < i; j++)
{
if (scan[j].flag)
insert(scan[j].y1, scan[j].y2, 0);
else
remove(scan[j].y1, scan[j].y2, 0);
if (j >= 1)
perimeter += 2*now_line*(scan[j].x - scan[j-1].x);
perimeter += abs(node[0].m - now_m);
now_m = node[0].m;
now_line = node[0].line;
}
printf("%d\n", perimeter);
return 0;
}