#include<stdio.h>
#include<math.h>
#define Nmax 2005
#define eps .000001

int N,X[Nmax],Y[Nmax],N1,N2;
double X1[Nmax],Y1[Nmax],X2[Nmax],Y2[Nmax];
double ang[Nmax];

int main()
{
FILE *fin=fopen("camera.in","r"),
     *fout=fopen("camera.out","w");
     
int i,j,k,Xmin=100000,Xmax=-100000,Ymin=100000,Ymax=-100000;
double aux;

fscanf(fin,"%d",&N);
for(i=1;i<=N;i++)
  fscanf(fin,"%d%d",&X[i],&Y[i]);
  
/*
for(i=1;i<=N/2;i++)
   {
   X[i]^=X[N-i+1], X[N-i+1]^=X[i], X[i]^=X[N-i+1];
   Y[i]^=Y[N-i+1], Y[N-i+1]^=Y[i], Y[i]^=Y[N-i+1];
   }
*/
//solve
for(i=1;i<=N;i++)
  {
  if(X[i] < Xmin) Xmin=X[i];
  if(X[i] > Xmax) Xmax=X[i];
  
  if(Y[i] < Ymin) Ymin=Y[i];
  if(Y[i] > Ymax) Ymax=Y[i];               
  }

//init  

N1=4;
X1[1]=(double)Xmin; Y1[1]=(double)Ymax;
X1[2]=(double)Xmin; Y1[2]=(double)Ymin;
X1[3]=(double)Xmax; Y1[3]=(double)Ymin;
X1[4]=(double)Xmax; Y1[4]=(double)Ymax;

X[N+1]=X[1],Y[N+1]=Y[1];

//aflare poligon intersectie
double Xi,Yi,A1,B1,C1,vc,vu,A2,B2,C2,det;

for(i=1;i<=N;i++)
  {
  A1=(double)Y[i+1] - Y[i];
  B1=(double)X[i] - X[i+1];
  C1=A1*X[i]+B1*Y[i];
  //pentru a fi in interior -> <0
  
  N2=0;
  X1[N1+1]=X1[1]; Y1[N1+1]=Y1[1];    
  for(j=1;j<=N1;j++) 
     {
     vc=A1*X1[j]+B1*Y1[j]-C1;
     vu=A1*X1[j+1]+B1*Y1[j+1]-C1;
     
     if(vc<=eps && vu<=eps)
        {
        X2[++N2]=X1[j];
        Y2[N2]=Y1[j];     
        }
     else
     if(vc<=eps && vu > eps)
        {
        X2[++N2]=X1[j];
        Y2[N2]=Y1[j];     
        
        if( -vc > eps )
            {//punctul de intersectie
             A2=Y1[j+1]-Y1[j];
             B2=X1[j]-X1[j+1];
             C2=A2*X1[j] + B2*Y1[j];
             
             det= A1*B2 - A2*B1;             
             Xi= (B2*C1 - B1*C2) / det;
             Yi= (A1*C2 - A2*C1) / det;
             
             X2[++N2]=Xi;
             Y2[N2]=Yi;                             
            }        
        }
      else
      if(vc >= eps && vu <= eps)
         {//doar punctul de intersectie
             A2=Y1[j+1]-Y1[j];
             B2=X1[j]-X1[j+1];
             C2=A2*X1[j] + B2*Y1[j];
             
             det= A1*B2 - A2*B1;             
             Xi= (B2*C1 - B1*C2) / det;
             Yi= (A1*C2 - A2*C1) / det;
             
             X2[++N2]=Xi;
             Y2[N2]=Yi;                             
         }
     }                 
  
  N1=N2;
  for(j=1;j<=N1;j++) 
      X1[j]=X2[j], Y1[j]=Y2[j];   
  }
  
// aria poligonului rezultat
double area=0.0;
for(i=2;i<N1;i++)
   {
   A1= X1[i] - X1[1];
   B1= Y1[i] - Y1[1];
   A2= X1[i+1] - X1[1];
   B2= Y1[i+1] - Y1[1];
   area+= A1*B2 - A2*B1;
   }
if(area>0.0)
  area /= 2.0;
else
  area /= -2.0;

fprintf(fout,"%.2f\n",area);

fclose(fin);
fclose(fout);
return 0;
}