AREA

//Nguyen Huu Hoang Minh
#include <bits/stdc++.h>
#define sz(x) int(x.size())
#define all(x) x.begin(),x.end()
#define reset(x) memset(x, 0,sizeof(x))
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define N 30100
#define remain(x) if (x > MOD) x -= MOD
#define ii pair<int, int>
#define iiii pair< ii , ii >
#define viiii vector< iiii >
#define vi vector<int>
#define vii vector< ii >
#define bit(x, i) (((x) >> (i)) & 1)
#define Task "test"
#define int long long

using namespace std;

typedef long double ld;
const int inf = 1e10;
const int minf = -1e10;

int n;
struct node{
    int x, u, d, t;
};
struct tree{
    int len, cnt;
};
node a[N];
tree tr[N*5];

bool cmp(node a, node b)
{
    return (a.x < b.x || (a.x==b.x && a.t < b.t));
}

void readfile()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    if (fopen(Task".inp","r"))
    {
        freopen(Task".inp","r",stdin);
        //freopen(Task".out","w",stdout);
    }
    cin >> n;
    for(int i=1; i<=n; i++)
    {
        int x1, y1, x2, y2;
        cin >> x1 >> y1 >> x2 >> y2;
        a[i].x = x1;
        a[i+n].x = x2;
        a[i].d = a[i+n].d = y1;
        a[i].u = a[i+n].u = y2;
        a[i].t = 1;
        a[i+n].t = -1;
    }
    n*=2;
    sort(a+1,a+1+n,cmp);
    //for(int i=1; i<=n; i++) cout << a[i].x << ' ' << a[i].u << ' ' << a[i].d << endl;
}

void up(int id, int l, int r, int u, int v, int ty)
{
    if (r < u || v < l) return;
    if (u <= l && r <= v)
    {
        tr[id].cnt += ty;
        //canh mo
        if (ty==1)
        {
            cout << l << ' ' << r << endl;
            tr[id].len = (r-l+1);
            //do dai
        }
        else{
            if (tr[id].cnt==0)
                tr[id].len = tr[id*2].len + tr[id*2+1].len;
        }
        return;
    }
    int mid = (l+r)/2;
    up(id*2,l,mid,u,v,ty);
    up(id*2+1,mid+1,r,u,v,ty);

    if (tr[id].cnt==0) tr[id].len = tr[id*2].len + tr[id*2+1].len;
}

void proc()
{
    int ans = 0;
    for(int i=1; i<=n; i++)
    {
        ans += (a[i].x-a[i-1].x)*(tr[1].len);
        //cout << a[i].d << ' ' << a[i].u-1 << ": \n";
        up(1,0,N, a[i].d, a[i].u-1, a[i].t);
    }
    cout << ans;
}

signed main()
{
    readfile();
    proc();
    return 0;
}