#include "bits/stdc++.h"
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;

using ll = long long;

int main() {
    int N;
    cin >> N;
    vector<int> x1(N), y1(N), x2(N), y2(N), xv, yv;
    set<int> xs, ys;
    rep(i, N) {
        cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
        xs.insert(x1[i]);
        xs.insert(x2[i]);
        ys.insert(y1[i]);
        ys.insert(y2[i]);
    }
    for (auto i : xs) xv.push_back(i);
    for (auto i : ys) yv.push_back(i);
    map<int, int> xm, ym;
    int m = xv.size(), n = yv.size();
    rep(i, xv.size()) xm[xv[i]] = i;
    rep(i, yv.size()) ym[yv[i]] = i;
    vector<vector<int>> d(m + 1, vector<int>(n + 1, 0));
    rep(i, N) {
        d[xm[x1[i]]][ym[y1[i]]]++;
        d[xm[x1[i]]][ym[y2[i]]]--;
        d[xm[x2[i]]][ym[y1[i]]]--;
        d[xm[x2[i]]][ym[y2[i]]]++;
    }
    /*
    rep(i, m + 1) {
        rep(j, n + 1) {
            cout << d[i][j];
        }
        cout << "\n";
    }
    cout << "\n";
    */
    vector<vector<int>> s(m + 1, vector<int>(n + 1, 0));
    rep(i, m) {
        rep(j, n) {
            s[i][j + 1] = s[i][j] + d[i][j];
        }
    }
    /*
    rep(i, m + 1) {
        rep(j, n + 1) {
            cout << s[i][j];
        }
        cout << "\n";
    }
    cout << "\n";
    */
    vector<vector<int>> t(m + 1, vector<int>(n + 1, 0));
    rep(j, n) {
        rep(i, m) {
            t[i + 1][j] = t[i][j] + s[i][j];
        }
    }
    /*
    rep(i, m + 1) {
        rep(j, n + 1) {
            cout << t[i][j];
        }
        cout << "\n";
    }
    cout << "\n";
    */
    ll ans = 0;
    rep(i, m - 1) {
        rep(j, n - 1) {
            if (t[i + 1][j + 1] > 0) {
                ans += 1LL * (xv[i + 1] - xv[i]) * (yv[j + 1] - yv[j]);
            }
        }
    }
    cout << ans << "\n";
    /*
    rep(i, m) cout << xv[i] << " ";
    cout << "\n";
    rep(i, n) cout << yv[i] << " ";
    cout << "\n";
    */
}
