时间复杂度 $O(n^2)$
注意：线段列表在合并后需要更新，不然会导致判断横纵线段交点时多判

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        ArrayList<Seg> rows = new ArrayList<>();
        ArrayList<Seg> cols = new ArrayList<>();

        for (int i = 0; i < n; ++i) {
            int x1 = scanner.nextInt();
            int y1 = scanner.nextInt();
            int x2 = scanner.nextInt();
            int y2 = scanner.nextInt();
            if (x1 == x2) {
                cols.add(new Seg(x1, Math.min(y1, y2), Math.max(y1, y2)));
            } else {
                rows.add(new Seg(y1, Math.min(x1, x2), Math.max(x1, x2)));
            }
        }
        long res = merge(rows) + merge(cols);
        for (Seg row : rows) {
            for (Seg col : cols) {
                if (row.k >= col.l && row.k <= col.r && col.k >= row.l && col.k <= row.r) {
                    --res;
                }
            }
        }
        System.out.println(res);
    }

    public static long merge(ArrayList<Seg> list) {
        long res = 0;
        ArrayList<Seg> temp = new ArrayList<>();
        list.sort((s1, s2) -> {
            if (s1.k != s2.k) {
                return s1.k - s2.k;
            } else if (s1.l != s2.l) {
                return s1.l - s2.l;
            } else {
                return s1.r - s2.r;
            }
        });
        for (int i = 0; i < list.size(); ) {
            int j = i;
            int l = Integer.MIN_VALUE + 1;
            int r = Integer.MIN_VALUE;
            while (j < list.size() && list.get(j).k == list.get(i).k) {
                ++j;
            }
            for (int k = i; k < j; ++k) {
                if (r < list.get(k).l) {
                    res += r - l + 1;
                    if (l != Integer.MIN_VALUE + 1) {
                        temp.add(new Seg(list.get(i).k, l, r));
                    }
                    r = list.get(k).r;
                    l = list.get(k).l;
                } else {
                    r = Math.max(r, list.get(k).r);
                }
            }
            res += r - l + 1;
            if (l != Integer.MIN_VALUE + 1) {
                temp.add(new Seg(list.get(i).k, l, r));
            }
            i = j;
        }
        list.clear();
        list.addAll(temp);
        return res;
    }

    static class Seg {
        int k;
        int l;
        int r;

        Seg(int k, int l, int r) {
            this.k = k;
            this.l = l;
            this.r = r;
        }
    }
}