#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
#include <cmath>
#define mem(a, b) memset(a, b, sizeof(a))
using namespace std;
const int maxn = 10010, INF = 0x7fffffff;
int X[maxn];struct node{int l, r, w; // l 和 r 分别为线段树的左右端点  w记录边重叠的情况int numseg;  // 记录竖边的对数int lx, rx, sum;  // sum代表当前区间线段的长度，lx和rx为线段的真实端点bool lcover, rcover;  // 标记当前区间的左右端点 与 numseg有关
}Node[maxn*4];struct edge{  // 存边int lxx, rxx, y;int f;
}Edge[maxn];int cmp(edge a, edge b)
{return a.y < b.y;
}void build(int k, int ll, int rr)
{Node[k].l = ll, Node[k].r = rr;Node[k].lx = X[ll];Node[k].rx = X[rr];Node[k].w = Node[k].numseg = 0, Node[k].sum = 0;Node[k].lcover = Node[k].rcover = false;if(ll + 1 == rr) return;int m = (ll + rr) / 2;build(k*2, ll, m);build(k*2+1, m, rr);
}void down(int k)
{if(Node[k].w > 0){Node[k].sum = Node[k].rx - Node[k].lx;Node[k].numseg = 1;Node[k].lcover = Node[k].rcover = true;return;}if(Node[k].l + 1 == Node[k].r){Node[k].sum = 0;Node[k].numseg = 0;Node[k].lcover = Node[k].rcover = false;}else{Node[k].sum = Node[k*2].sum + Node[k*2+1].sum;Node[k].lcover = Node[k*2].lcover, Node[k].rcover = Node[k*2+1].rcover;Node[k].numseg = Node[k*2].numseg + Node[k*2+1].numseg;if(Node[k*2].rcover && Node[k*2+1].lcover) Node[k].numseg--;   //注意这里是左区间的右端点 和 右区间的左端点
    }
}void update(int k, edge e)
{if(Node[k].lx == e.lxx && Node[k].rx == e.rxx){Node[k].w += e.f;down(k);return;}if(e.rxx <= Node[k*2].rx) update(k*2, e);else if(e.lxx >= Node[k*2+1].lx) update(k*2+1, e);else{edge temp = e;temp.rxx = Node[k*2].rx;update(k*2, temp);temp = e;temp.lxx = Node[k*2+1].lx;update(k*2+1, temp);}down(k);
}int main()
{int n, cnt = 0;scanf("%d",&n);for(int i=0; i<n; i++){int x1, x2, y1, y2;scanf("%d%d%d%d",&x1,&y1,&x2,&y2);Edge[++cnt].lxx = x1, Edge[cnt].rxx = x2, Edge[cnt].y = y1, Edge[cnt].f = 1;X[cnt] = x1;Edge[++cnt].lxx = x1, Edge[cnt].rxx = x2, Edge[cnt].y = y2, Edge[cnt].f = -1;X[cnt] = x2;}sort(Edge+1, Edge+cnt+1, cmp);sort(X+1, X+cnt+1);int m = unique(X+1, X+cnt+1) - (X+1);build(1, 1, m);int ret = 0, last = 0;for(int i=1; i<cnt; i++){update(1, Edge[i]);ret += abs(Node[1].sum - last); // 横边ret += Node[1].numseg * 2 * (Edge[i+1].y - Edge[i].y);  // 加竖边last = Node[1].sum;}update(1, Edge[cnt]);ret += abs(Node[1].sum - last);printf("%d\n",ret);return 0;
}