#include <iostream>

#include <cstring>

#include <cstdio>

#include <algorithm>

#define maxn 220000

#define lson l,m,rt << 1

#define rson m + 1,r,rt << 1 | 1

#define eps 1e-15

using namespace std;

struct seg

{

    double l,r,y;

    int sign;

    seg() {}

    seg(double a, double b, double h, int s): l(a), r(b),y(h),sign(s) {}

    bool operator < (const seg &cmp) const

    {

        if(cmp.y == y) return sign > cmp.sign;

        return y < cmp.y;

    }

} p[ (maxn <<  )+ ];

double sum[ (maxn <<  )+ ];

int cnt[ (maxn << ) + ];

double X[ (maxn << ) + ];

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

{

    if(cnt[rt]) sum[rt] = X[r + ] - X[l];

    else if(l == r) sum[rt] = 0.0;

    else    sum[rt] = sum[rt << ] + sum[rt <<  | ];

}

void update(int L, int R, int cc, int l , int r, int rt)

{

    if(L <= l && r <= R)

    {

        cnt[rt] += cc;

        push_up(rt,l,r);

        return ;

    }

    int m = (l + r) >> ;

    if(L <= m) update(L,R,cc,lson);

    if(R > m)   update(L,R,cc,rson);

    push_up(rt,l,r);

}

int bin(int low, int high, double key)

{

    int mid ;

    while(low < high)

    {

        mid = (low + high) >> ;

        if(X[mid] < key ) low = mid + ;

        else high = mid;

    }

    return low;

}

int main()

{

    int n,m,k,pp,ca = ;

    double a,b,c,d,ret;

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

    {

        memset(sum,,sizeof(sum));

        memset(cnt,,sizeof(cnt));

        m = k = ;

        ret = 0.0;

        pp = ;

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

        {

            scanf("%lf%lf%lf%lf",&a,&b,&c,&d);

            if(b==d)

            {

                if(a>c) swap(a,c);

            }

            else if(a==c)

            {

                if(b>d) swap(b,d);

            }

            c++;

            d++;

            X[m ++] = a;

            X[m ++] = c;

            p[k ++] = seg(a,c,b,);

            p[k ++] = seg(a,c,d,-);

        }

        sort(X,X + m);

        sort(p,p + k);

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

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

            {

                X[pp ++] = X[i];

            }

        pp --;

        for(int i = ; i < k - ; i ++)

        {

            int l = bin(, pp , p[i].l);

            int r = bin(, pp , p[i].r) - ;

            if(l <= r) update(l,r,p[i].sign,,pp,);

            ret += (p[i + ].y - p[i].y) * sum[];

        }

        printf("%.0f\n",ret);

    }

    return ;

}