#include<bits/stdc++.h>
using namespace std;
int ls(int p)
{
    return p<<1;
}
int rs(int p)
{
    return p<<1|1;
}
const int N=200005;
struct Scanline
{
    int l, r, h, inout;
    Scanline(){}
    Scanline(int a, int b, int c, int d):l(a),r(b),h(c),inout(d){}
}line[N];
bool cmp(Scanline &a, Scanline &b)
{
    return a.h<b.h||a.h==b.h&&a.inout>b.inout;
}
bool lbd[N<<2], rbd[N<<2];
int num[N<<2], tag[N<<2], length[N<<2];
void pushup(int p, int pl, int pr)
{
    if(tag[p])
    {
        lbd[p]=rbd[p]=1;
        length[p]=pr-pl+1;
        num[p]=1;
    }
    else if(pl==pr)
    {
        length[p]=num[p]=lbd[p]=rbd[p]=0;
    }
    else
    {
        lbd[p]=lbd[ls(p)];
        rbd[p]=rbd[rs(p)];
        length[p]=length[ls(p)]+length[rs(p)];
        num[p]=num[ls(p)]+num[rs(p)];
        if(lbd[rs(p)]&&rbd[ls(p)])
        {
            num[p]=-1;
        }
    }
    return ;
}
void update(int L, int R, int io, int p, int pl, int pr)
{
    if(L<=pl&&pr<=R)
    {
        tag[p]+=io;
        pushup(p,pl,pr);
        return ;
    }
    int mid=(pl+pr)>>1;
    if(L<=mid)
    {
        update(L,R,io,ls(p),pl,mid);
    }
    if(mid<R)
    {
        update(L,R,io,rs(p),mid+1,pr);
    }
    pushup(p,pl,pr);
}
int main()
{
    long long n, jntm=0;
    while(~scanf("%d",&n))
    {
        
        int cnt=0;
        int lbd=10000, rbd=-10000;
        for(int i=0;i<n;i++)
        {
            int x1, y1, x2, y2;
            scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
            lbd=min(lbd,x1);
            rbd=max(rbd,x2);
            line[++cnt]=Scanline(x1,x2,y1,1);
            line[++cnt]=Scanline(x1,x2,y2,-1);
        }
        sort(line+1,line+cnt+1,cmp);
        int ans=0, last=0;
        for(int i=1;i<=cnt;i++)
        {
            if(line[i].l<line[i].r)
            {
                update(line[i].l,line[i].r-1,line[i].inout,1,lbd,rbd-1);
            }
            ans+=num[1]*2*(line[i+1].h-line[i].h);
            ans+=abs(length[1]-last);
            last=length[1];
        }
        cout<<ans<<"\n";
    }
    return 0;
}