Given a set of $N$ axis-aligned rectangles in the plane, find the area of regions which are covered by at least one rectangle.

Constraints

* $ 1 \leq N \leq 2000 $
* $ −10^9 \leq x1_i < x2_i\leq 10^9 $
* $ −10^9 \leq y1_i < y2_i\leq 10^9 $

Input

The input is given in the following format.

$N$
$x1_1$ $y1_1$ $x2_1$ $y2_1$
$x1_2$ $y1_2$ $x2_2$ $y2_2$
:
$x1_N$ $y1_N$ $x2_N$ $y2_N$


($x1_i, y1_i$) and ($x2_i, y2_i$) are the coordinates of the top-left corner and the bottom-right corner of the $i$-th rectangle respectively.

Output

Print the area of the regions.

Examples

Input

2
0 0 3 4
1 2 4 3


Output

13


Input

3
1 1 2 5
2 1 5 2
1 2 2 5


Output

7


Input

4
0 0 3 1
0 0 1 3
0 2 3 3
2 0 3 3


Output

8
#include <bits/stdc++.h>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using ll = long long;
using P = pair<int, int>;

int main() {
  int n;
  cin >> n;
  vector<int> x1(n), y1(n), x2(n), y2(n);
  vector<int> X,Y;
  rep(i,n) {
    cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
    X.push_back(x1[i]);
    X.push_back(x2[i]);
    Y.push_back(y1[i]);
    Y.push_back(y2[i]);
  }
  sort(X.begin(), X.end());
  sort(Y.begin(), Y.end());
  X.erase(unique(X.begin(),X.end()),X.end());
  Y.erase(unique(Y.begin(),Y.end()),Y.end());

  int xs = X.size();
  int ys = Y.size();

  vector< vector<int> > imos(xs, vector<int>(ys));
  rep(i,n) {
    x1[i] = lower_bound(X.begin(), X.end(), x1[i]) - X.begin();
    x2[i] = lower_bound(X.begin(), X.end(), x2[i]) - X.begin();
    y1[i] = lower_bound(Y.begin(), Y.end(), y1[i]) - Y.begin();
    y2[i] = lower_bound(Y.begin(), Y.end(), y2[i]) - Y.begin();
    imos[x1[i]][y1[i]]++;
    imos[x1[i]][y2[i]]--;
    imos[x2[i]][y1[i]]--;
    imos[x2[i]][y2[i]]++;
  }
  rep(i,xs) rep(j,ys-1) imos[i][j+1] += imos[i][j];
  rep(i,xs-1) rep(j,ys) imos[i+1][j] += imos[i][j];

  ll ans = 0;
  rep(i,xs-1) rep(j,ys-1) {
    if (imos[i][j]==0) continue;
    ans += (ll)(X[i+1]-X[i])*(Y[j+1]-Y[j]);
  }

  cout << ans << endl;

  return 0;
}
