//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<cmath>
#include<climits>
#include<string>
#include<map>
#include<queue>
#include<vector>
#include<stack>
#include<set>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define pb(a) push_back(a)
#define INF 0x1f1f1f1f
#define lson idx<<1,l,mid
#define rson idx<<1|1,mid+1,r
#define PI  3.1415926535898
template<class T> T min(const T& a,const T& b,const T& c) {return min(min(a,b),min(a,c));
}
template<class T> T max(const T& a,const T& b,const T& c) {return max(max(a,b),max(a,c));
}
void debug() {
#ifdef ONLINE_JUDGE
#elsefreopen("d:\\in.txt","r",stdin);// freopen("d:\\out1.txt","w",stdout);
#endif
}
int getch() {int ch;while((ch=getchar())!=EOF) {if(ch!=' '&&ch!='\n')return ch;}return EOF;
}
const int maxn=5000;
struct Seg
{double a,b,x;int c;Seg(){}Seg(double a,double b,double c,int d):a(a),b(b),x(c),c(d){}bool operator < (const Seg& another) const{return x<another.x;}
};
Seg seg[maxn<<1];
double Y[maxn<<1];
int num[maxn<<3];
int flag[maxn<<3];
int point[maxn<<3][2];
double sum[maxn<<3];
int build(int idx,int l, int r)
{memset(num,0,sizeof(num));memset(flag,0,sizeof(flag));memset(point,0,sizeof(point));memset(sum,0,sizeof(sum));return 0;
}
int PushUp(int idx,int l,int r)
{if(flag[idx]){num[idx]=2;point[idx][0]=point[idx][1]=1;sum[idx]=Y[r+1]-Y[l];}else if(l!=r){num[idx]=num[idx<<1]+num[idx<<1|1];if(point[idx<<1][1]&&point[idx<<1|1][0])num[idx]-=2;point[idx][0]=point[idx<<1][0];point[idx][1]=point[idx<<1|1][1];sum[idx]=sum[idx<<1]+sum[idx<<1|1];}else{num[idx]=0;point[idx][0]=point[idx][1]=0;sum[idx]=0;}return 0;
}
int update(int idx,int l,int r,int tl,int tr,int v)
{if(tl<=l&&tr>=r){flag[idx]+=v;PushUp(idx,l,r);return 0;}int mid=(r+l)>>1;if(tl<=mid)update(lson,tl,tr,v);if(tr>mid)update(rson,tl,tr,v);PushUp(idx,l,r);return 0;
}
int main()
{int n;while(scanf("%d",&n)!=EOF){int m=0;for(int i=0;i<n;i++){double a,b,c,d;scanf("%lf%lf%lf%lf",&a,&b,&c,&d);seg[m]=Seg(b,d,a,1);Y[m++]=b;seg[m]=Seg(b,d,c,-1);Y[m++]=d;}sort(seg,seg+m);sort(Y,Y+m);int k=1;for(int i=1;i<m;i++)if(Y[i]!=Y[i-1])Y[k++]=Y[i];double res=0;build(1,0,k);for(int i=0;i<m;i++){if(i!=0)res+=(seg[i].x-seg[i-1].x)*num[1];int l=lower_bound(Y,Y+k,seg[i].a)-Y;int r=lower_bound(Y,Y+k,seg[i].b)-Y;double last=sum[1];update(1,0,k,l,r-1,seg[i].c);res+=fabs(sum[1]-last);}printf("%d\n",int(res+0.00001));}return 0;
}