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<vector>
#include<algorithm>
#include<utility>
using namespace std;

template<class T>
class CoordinateCompression{
    vector<T> dat;
    int s;
    int n;

public:
    CoordinateCompression(const vector<T>& dat_, int s_ = 0){
        build(dat_, s_);
    }

    void build(const vector<T>& dat_, int s_ = 0){
        dat = dat_;

        sort(dat.begin(), dat.end());
        dat.erase(unique(dat.begin(), dat.end()), dat.end());

        s = s_;

        n = (int)dat.size();

        return;
    }

    int get(T x){
        return (int)(lower_bound(dat.begin(), dat.end(), x) - dat.begin()) + s;
    }

    T restore(int k){
        return dat[k - s];
    }

    int size(void){
        return n;
    }
};

#include<iostream>

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n;
    cin >> n;

    vector<int> x1(n), y1(n), x2(n), y2(n);
    vector<int> xs, ys;
    for(int i = 0 ; i < n ; ++i){
        cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];
        xs.emplace_back(x1[i]);
        xs.emplace_back(x2[i]);
        ys.emplace_back(y1[i]);
        ys.emplace_back(y2[i]);
    }

    CoordinateCompression<int> x(xs), y(ys);

    vector< vector<int> > imos(y.size(), vector<int>(x.size()));
    for(int i = 0 ; i < n ; ++i){
        int sy = y.get(y1[i]);
        int sx = x.get(x1[i]);
        int gy = y.get(y2[i]);
        int gx = x.get(x2[i]);
        ++imos[sy][sx];
        --imos[sy][gx];
        --imos[gy][sx];
        ++imos[gy][gx];
    }

    for(int i = 0 ; i < y.size() ; ++i){
        for(int j = 1 ; j < x.size() ; ++j){
            imos[i][j] += imos[i][j - 1];
        }
    }

    for(int j = 0 ; j < x.size() ; ++j){
        for(int i = 1 ; i < y.size() ; ++i){
            imos[i][j] += imos[i - 1][j];
        }
    }

    long long ans = 0;
    for(int i = 0 ; i < y.size() - 1 ; ++i){
        for(int j = 0 ; j < x.size() - 1 ; ++j){
            if(imos[i][j] > 0){
                ans += ((long long)y.restore(i + 1) - y.restore(i)) * ((long long)x.restore(j + 1) - x.restore(j));
            }
        }
    }

    cout << ans << endl;

    return 0;
}
