#include <bits/stdc++.h>
using namespace std;

typedef long long LL;
const int N = 1e6 + 10;
LL res;
int n;
int b[N];

// 横版
struct ScanLine {
    int x1, x2, y, mark;
    const bool operator<(const ScanLine &t) {
        return y < t.y;
    }
} line[N << 1];

struct Node {
    int l, r;
    int len;
    int cnt;
} tr[N << 2];

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

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);
}

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);
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("P5490.in", "r", stdin);
#endif
    ios::sync_with_stdio(false), cin.tie(0);
    cin >> n;
    int x1, x2, y1, y2;
    for (int i = 1; i <= n; i++) {
        cin >> x1 >> y1 >> x2 >> y2;
        b[i * 2 - 1] = x1, b[i * 2] = x2;
        line[i * 2 - 1] = {x1, x2, y1, 1};
        line[i * 2] = {x1, x2, y2, -1};
    }

    n *= 2;
    sort(line + 1, line + n + 1);
    sort(b + 1, b + n + 1);
    int tot = unique(b + 1, b + n + 1) - b - 1;
    build(1, 1, tot - 1);

    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].len * (line[i + 1].y - line[i].y);
    }

    printf("%lld\n", res);
    return 0;
}