#include <cstdio>
#include <algorithm>
#include <utility>
#include <cmath>

using namespace std;

pair <double, int> l[1000000];

struct Point
{
  double x, y;
  Point() {}
  Point(double a, double b) {x = a, y = b;}
};

double Less(Point a, Point b)
{
  return (a.first < a.first);
}

int main()
{
  int n, i, k = 0;
  double s = 0, r1, r2, lf = 0;
  double rmin = 1000001, rmax = 0;
  scanf("%d", &n);
  for ( i = 0; i < n; i++)
  {
    scanf("%lf %lf %lf %lf", &r1, &r2, &l[2 * i].first, &l[2 * i + 1].first);
    rmin = min(rmin, r1);
    rmax = max(rmax, r2);
    l[2 * i].second = 1;
    l[2 * i + 1].second = 2;
    if ( l[2 * i].first > l[2 * i + 1].first )
    {
      k++;
      lf = max(lf, l[2 * i].first);
    }
  }
  sort(l, l + 2 * n, Less);
  for ( i = 1; i < 2 * n; i++)
  {
    if ( k == n)
    {
      s += ((l[i].first - lf) * rmax * rmax - (l[i].first - lf) * rmin * rmin) / 2;
      lf = l[i].first;
    }
    if ( l[i].second == 1)
    {
      k++;
      lf = l[i].first;
    }
  }
  printf("%10.lf", s);
  return 0;
}