var n,i:word;
   s:real;
   a,b:array[1..60010] of int64;
begin
    read(a[1],b[1],a[2],b[2],a[3],b[3],a[4],b[4]);
   for i:=2 to 3 do
    s:=s+((a[i]-a[1])*(b[i+1]-b[1])-(b[i]-b[1])*(a[i+1]-a[1]));
   s:=abs(s/2);
   writeln(s:0:0)
end.