const

     maxn=;

     eps=1e-7;

 type

     point=record

       x,y:double;

     end;

     poly=record

       x,y,w:point;

     end;

 var

     a:array[..maxn]of poly;

     n:longint;

 operator -(a,b:point)c:point;

 begin

     c.x:=a.x-b.x;

     c.y:=a.y-b.y;

 end;

 operator +(a,b:point)c:point;

 begin

     c.x:=a.x+b.x;

     c.y:=a.y+b.y;

 end;

 operator *(a:point;b:double)c:point;

 begin

     c.x:=a.x*b;

     c.y:=a.y*b;

 end;

 operator *(a,b:point)c:double;

 begin

     c:=a.x*b.y-a.y*b.x;

 end;

 function wh(a:point):longint;

 begin

     with a do

       begin

         if abs(x)<eps then

           if y>eps then exit()

           else exit()

         else

           if abs(y)<eps then

             if x>eps then exit()

             else exit()

           else

             if x>eps then

               if y>eps then exit()

               else exit()

             else

               if y>eps then exit()

               else exit();

       end;

 end;

 procedure swap(var x,y:poly);

 var

     t:poly;

 begin

     t:=x;x:=y;y:=t;

 end;

 procedure sort(l,r:longint);

 var

     i,j:longint;

     y:point;

 begin

     i:=l;

     j:=r;

     y:=a[(l+r)>>].w;

     repeat

       while (wh(a[i].w)<wh(y)) or ((wh(a[i].w)=wh(y)) and (y*a[i].w+eps<)) do

         inc(i);

       while (wh(a[j].w)>wh(y)) or ((wh(a[j].w)=wh(y)) and (y*a[j].w>eps)) do

         dec(j);

       if i<=j then

       begin

         swap(a[i],a[j]);

         inc(i);

         dec(j);

       end;

     until i>j;

     if i<r then sort(i,r);

     if j>l then sort(l,j);

 end;

 procedure init;

 var

     i:longint;

 begin

     read(n);

     for i:= to n do

       with a[i] do

         begin

           read(x.x,x.y,y.x,y.y);

           w:=y-x;

         end;

     a[n+].x.x:=;

     a[n+].x.x:=;

     a[n+].x.y:=;

     a[n+].x.y:=;

     for i:= to  do

       begin

         a[n+i+].y:=a[n+((i+)mod )+].x;

         a[n+i+].w:=a[n+i+].y-a[n+i+].x;

       end;

     inc(n,);

     sort(,n);

 end;

 function get(a,b:poly):point;

 var

     s1,s2:double;

 begin

     s1:=a.w*(b.y-a.x);

     s2:=a.w*(b.x-a.x);

     if s1*s2>eps then s1:=-s1

     else

       begin

         s1:=abs(s1);

         s2:=abs(s2);

       end;

     if abs(s1+s2)<eps then get:=b.x

     else get:=b.x+(b.w*(s2/(s1+s2)));

 end;

 var

     q:array[..maxn]of poly;

     d:array[..maxn]of point;

     l,r:longint;

     ans:double;

 procedure work;

 var

     i:longint;

 begin

     l:=;

     r:=;

     q[]:=a[];

     for i:= to n do

       begin

         while (l<r) and (a[i].w*(d[r-]-a[i].x)+eps<) do

           dec(r);

         while (l<r) and (a[i].w*(d[l]-a[i].x)+eps<) do

           inc(l);

         inc(r);

         q[r]:=a[i];

         if abs(q[r-].w*q[r].w)<eps then

         begin

           dec(r);

           if a[i].w*(q[r].x-a[i].x)< then q[r]:=a[i];

         end;

         d[r-]:=get(q[r],q[r-]);

       end;

     while (l<r) and (q[l].w*(d[r-]-q[l].x)+eps<) do

       dec(r);

     if l<r then d[r]:=get(q[l],q[r]);

     if r-l<= then writeln('0.0')

     else

       begin

         for i:=l to r- do

           ans:=ans+(d[i]*d[i+])/;

         ans:=ans+(d[r]*d[l])/;

         ans:=abs(ans);

         if ans<eps then writeln('0.0')

         else writeln(ans::);

       end;

 end;

 begin

     init;

     work;

 end.