#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N = 10010;

struct ScanLine {
    int x1, x2, y, mark;
    const bool operator<(const ScanLine &t) const {
        if (y == t.y) return mark > t.mark;
        return y < t.y;
    }

} line[N];

struct Node {
    int l, r;
    int cnt, len;
    int c;
    bool lc, rc;

} tr[N << 2];

int b[N];

void pushup(int u) {
    int l = tr[u].l, r = tr[u].r;
    if (tr[u].cnt) {
        tr[u].len = b[r + 1] - b[l];
        tr[u].c = 2;
        tr[u].lc = tr[u].rc = 1;
    } else {
        tr[u].len = tr[u << 1].len + tr[u << 1 | 1].len;
        tr[u].c = tr[u << 1].c + tr[u << 1 | 1].c;
        if (tr[u << 1 | 1].lc && tr[u << 1].rc) tr[u].c -= 2;
        tr[u].lc = tr[u << 1].lc;
        tr[u].rc = tr[u << 1 | 1].rc;
    }
}

void modify(int u, int l, int r, int v) {
    if (l <= tr[u].l && r >= tr[u].r) {
        tr[u].cnt += v;
        pushup(u);
        return;
    }
    int mid = (tr[u].l + tr[u].r) >> 1;
    if (l <= mid) modify(u << 1, l, r, v);
    if (r > mid) modify(u << 1 | 1, l, r, v);
    pushup(u);
}

void build(int u, int l, int r) {
    tr[u].l = l, tr[u].r = r;
    if (l == r) return;
    int mid = (l + r) >> 1;
    build(u << 1, l, mid);
    build(u << 1 | 1, mid + 1, r);
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("HDU1828.in", "r", stdin);
#endif

    ios::sync_with_stdio(false), cin.tie(0);
    int n;
    while (cin >> n) {
        memset(tr, 0, sizeof tr);
        int x1, y1, x2, y2;
        for (int i = 1; i <= n; i++) {
            cin >> x1 >> y1 >> x2 >> y2;
            line[i * 2 - 1] = {x1, x2, y1, 1};
            line[i * 2] = {x1, x2, y2, -1};
            b[i * 2 - 1] = x1, b[i * 2] = x2;
        }

        n <<= 1;

        sort(line + 1, line + n + 1);
        sort(b + 1, b + n + 1);
        int tot = unique(b + 1, b + 1 + n) - b - 1;

        build(1, 1, tot - 1);

        LL res = 0;
        int last = 0;

        for (int i = 1; i < n; i++) {
            int L = lower_bound(b + 1, b + tot + 1, line[i].x1) - b;
            int R = lower_bound(b + 1, b + tot + 1, line[i].x2) - b;
            modify(1, L, R - 1, line[i].mark);

            res += (LL)tr[1].c * (line[i + 1].y - line[i].y);
            res += (LL)abs(tr[1].len - last);
            last = tr[1].len;
        }
        res += line[n].x2 - line[n].x1;
        printf("%lld\n", res);
    }
    return 0;
}