#include <iostream>

#include <cmath>

#include <iostream>

#include <cstdio>

#include <cstring>

#include <cstdlib>

#include <cmath>

#include <algorithm>

using namespace std;

#define N 10007

struct node

{

    int cov,len,num,lmark,rmark;

}tree[*N];

struct Line

{

    int y1,y2,x;

    int cov;

}line[*N];

int yy[*N];

int cmp(Line ka,Line kb)

{

    return ka.x < kb.x;

}

int bsearch(int l,int r,int x)

{

    while(l <= r)

    {

        int mid = (l+r)/;

        if(x == yy[mid])

            return mid;

        if(x > yy[mid])

            l = mid+;

        else

            r = mid-;

    }

    return l;

}

void build(int l,int r,int rt)

{

    tree[rt].cov = tree[rt].len = tree[rt].num = tree[rt].lmark = tree[rt].rmark = ;

    if(l == r-) return;

    int mid = (l+r)/;

    build(l,mid,*rt);

    build(mid,r,*rt+);

}

void pushup(int l,int r,int rt)

{

    if(tree[rt].cov)

    {

        tree[rt].len = yy[r]-yy[l];

        tree[rt].lmark = tree[rt].rmark = ;

        tree[rt].num = ;

    }

    else if(l+ == r)

        tree[rt].len = tree[rt].num = tree[rt].lmark = tree[rt].rmark = ;

    else

    {

        tree[rt].len = tree[*rt].len + tree[*rt+].len;

        tree[rt].lmark = tree[*rt].lmark;

        tree[rt].rmark = tree[*rt+].rmark;

        tree[rt].num = tree[*rt].num+tree[*rt+].num-tree[*rt].rmark*tree[*rt+].lmark;

        //如果左右区间连续，那么可以合并，减少一个区间

    }

}

void update(int l,int r,int aa,int bb,int cover,int rt)

{

    if(aa <= l && bb >= r)

    {

        tree[rt].cov += cover;

        pushup(l,r,rt);

        return;

    }

    if(l+ == r) return;

    int mid = (l+r)/;

    if(aa <= mid)

        update(l,mid,aa,bb,cover,*rt);

    if(bb > mid)

        update(mid,r,aa,bb,cover,*rt+);

    pushup(l,r,rt);

}

int main()

{

    int n,m,cs = ,i,j;

    int x1,y1,x2,y2;

    while(scanf("%d",&n)!=EOF)

    {

        m = ;

        for(i=;i<n;i++)

        {

            scanf("%d%d%d%d",&x1,&y1,&x2,&y2);

            line[m].x = x1,line[m].y1 = y1,line[m].y2 = y2,line[m].cov = ,yy[m++] = y1;

            line[m].x = x2,line[m].y1 = y1,line[m].y2 = y2,line[m].cov = -,yy[m++] = y2;

        }

        m--;

        sort(yy+,yy+m+);

        int cnt = ;

        for(i=;i<=m;i++)

        {

            if(yy[i] != yy[i-])

                yy[cnt++] = yy[i];

        }

        cnt--;

        build(,cnt,);

        sort(line+,line+m+,cmp);

        int ans = ;

        int last = ;

        for(i=;i<=m;i++)

        {

            int L = bsearch(,cnt,line[i].y1);

            int R = bsearch(,cnt,line[i].y2);

            update(,cnt,L,R,line[i].cov,);

            ans += abs(last - tree[].len);

            if(i == m) break;

            ans += tree[].num**(line[i+].x-line[i].x);

            last = tree[].len;

        }

        printf("%d\n",ans);

    }

    return ;

}