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 <map>
#include <algorithm>
using namespace std;

template <typename T>
class compress {
private:
    map<T, size_t> zipped;
    vector<T> unzipped;

public:
    compress(vector<T> &X) {
        sort(begin(X), end(X));
        X.erase(unique(begin(X), end(X)), end(X));
        unzipped.resize(X.size());
        for(size_t i=0; i<X.size(); ++i) {
            zipped[X[i]] = i;
            unzipped[i] = X[i];
        }
    }

    size_t size() { return zipped.size(); }
    size_t zip(T x) { return zipped[x]; }
    T unzip(size_t x) { return unzipped[x]; }
};


#include <iostream>
#include <vector>
using namespace std;

int main() {
    int N; cin >> N;
    vector<int> x1(N), y1(N), x2(N), y2(N);
    for(int i=0; i<N; ++i) cin >> x1[i] >> y1[i] >> x2[i] >> y2[i];

    vector<int> X(x1);
    copy(begin(x2), end(x2), back_inserter(X));
    vector<int> Y(y1);
    copy(begin(y2), end(y2), back_inserter(Y));

    compress<int> xc(X), yc(Y);

    vector<vector<int>> accum(xc.size(), vector<int>(yc.size(), 0));
    for(int i=0; i<N; ++i) {
        accum[xc.zip(x1[i])][yc.zip(y1[i])] += 1;
        accum[xc.zip(x1[i])][yc.zip(y2[i])] -= 1;
        accum[xc.zip(x2[i])][yc.zip(y1[i])] -= 1;
        accum[xc.zip(x2[i])][yc.zip(y2[i])] += 1;
    }

    for(int i=0; i<xc.size(); ++i) {
        for(int j=1; j<yc.size(); ++j) {
            accum[i][j] += accum[i][j - 1];
        }
    }

    for(int i=1; i<xc.size(); ++i) {
        for(int j=0; j<yc.size(); ++j) {
            accum[i][j] += accum[i - 1][j];
        }
    }

    long long ans = 0;
    for(int i=0; i+1<xc.size(); ++i) {
        for(int j=0; j+1<yc.size(); ++j) {
            if(accum[i][j] > 0) {
                ans += 1LL * (xc.unzip(i + 1) - xc.unzip(i)) * (yc.unzip(j + 1) - yc.unzip(j));
            }
        }
    }

    cout << ans << endl;
}
