import java.awt.geom.Point2D;
import java.io.File;
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;
import java.util.TreeSet;

public class realeastate_artur {

  static double eps = 1e-9;

  static int dc(double x, double y) {
    if (Math.abs(x - y) < eps)
      return 0;
    return x < y ? -1 : 1;
  }

  public static void main(String[] args) throws Exception {
    Scanner in = new Scanner(System.in);
    PrintStream out = System.out;

    int n;
    while ((n = in.nextInt()) != 0) {
      double[] x1 = new double[n];
      double[] y1 = new double[n];
      double[] x2 = new double[n];
      double[] y2 = new double[n];

      TreeSet<Double> set = new TreeSet<Double>(new Comparator<Double>() {
        @Override
        public int compare(Double x, Double y) {
          return dc(x, y);
        }
      });

      for (int i = 0; i < n; i++) {
        x1[i] = in.nextDouble();
        y1[i] = in.nextDouble();
        x2[i] = in.nextDouble();
        y2[i] = in.nextDouble();

        set.add(x1[i]);
        set.add(x2[i]);
      }

      // Simple O(N*N*logN):
      // Sweep vertical line L and for each position  compute the overlapping length of y-segments in O(NlogN).
      double result = 0;
      double left, right = set.pollFirst(), mid;
      while (!set.isEmpty()) {
        left = right;
        right = set.pollFirst();
        mid = (left + right) / 2;

        ArrayList<Point2D.Double> yList = new ArrayList<Point2D.Double>();

        for (int i = 0; i < n; i++)
          if (dc(x1[i], mid) != 1 && dc(mid, x2[i]) != 1) {
            yList.add(new Point2D.Double(y1[i], -1));
            yList.add(new Point2D.Double(y2[i], 1));
          }

        Collections.sort(yList, new Comparator<Point2D.Double>() {
          @Override
          public int compare(Point2D.Double a, Point2D.Double b) {
            if (dc(a.x, b.x) == 0)
              return dc(a.y, b.y);
            return dc(a.x, b.x);
          }
        });

        double length = 0;
        int k = 0;
        for (int i = 0; i < yList.size(); i++) {
          if (k != 0 && i > 0)
            length += yList.get(i).x - yList.get(i - 1).x;
          if (yList.get(i).y > 0)
            k++;
          else
            k--;
        }

        result += length * (right - left);
      }

      out.printf("%.2f\n", result);
    }
  }
}