#include <iostream>
#include <vector>
#include <math.h>
#include <algorithm>
using namespace std ;
struct pt { 
   double len() const { return hypot(x, y) ; }
   double x, y ;
} ;
int main() {
   int N ;
   cin >> N ;
   vector<pt> poles(N) ;
   vector<double> ht(N), poleht(N), basearea(N) ;
   double x, y ;
   vector<pair<double, int> > sortable(N-1), areas(N-1) ;
   for (int i=1; i<N; i++) {
      cin >> x >> y ;
      poles[i] = {x, y} ;
      sortable[i-1] = make_pair(atan2(y, x), i) ;
   }
   sort(sortable.begin(), sortable.end()) ;
   for (int i=0; i<N; i++)
      cin >> ht[i] ;
   sort(ht.begin(), ht.end()) ;
   for (int i=0; i+1<N; i++) {
      int prev = (i + (N-1) - 1) % (N-1) ;
      int next = (i + (N-1) + 1) % (N-1) ;
      double angprev = sortable[i].first - sortable[prev].first ;
      double angnext = sortable[next].first - sortable[i].first ;
      double triangles = 0.5 * poles[sortable[i].second].len() *
                    (sin(angprev) * poles[sortable[prev].second].len() +
                     sin(angnext) * poles[sortable[next].second].len()) ;
      areas[i] = make_pair(triangles, i+1) ;
      basearea[i] = triangles ;
   }
   sort(areas.begin(), areas.end()) ;
   poleht[0] = ht[N-1] ;
   for (int i=0; i<N-1; i++)
      poleht[areas[i].second] = ht[i] ;
   double v = 0 ;
   for (int i=0; i<N-1; i++)
      v += (poleht[i+1] / 3 + poleht[0] / 6) * basearea[i] ;

   char answer[20];
   sprintf( answer, "%.2f", v );
   cout << answer << endl ;
}