#include <stdio.h>
#include <math.h>
#include <iostream>
struct Point{
	int x;
	int y;
};

struct Point CreatePoint(int,int);
float line(Point,Point);
float str(float,float,float);

int main(){
	Point A;
	Point B;
	Point C;
	Point D;
	scanf_s("%d%d%d%d", &A.x,&A.y,&B.x,&B.y);
	scanf_s("%d%d%d%d", &C.x,&C.y,&D.x,&D.y);
	A = CreatePoint(A.x,A.y);
	B = CreatePoint(B.x,B.y);
	C = CreatePoint(C.x,C.y);
	D = CreatePoint(D.x,D.y);
	float squa=str(line(A,B),line(B,C),line(C,A))+str(line(C,D),line(D,A),line(C,A));
	printf_s("%f",squa);
	system("pause");
	return 0;
}

struct Point CreatePoint(int x,int y){
	Point tmp;
	tmp.x = x;
	tmp.y = y;
	return tmp;
}
float line(Point a,Point b){
	float l = sqrt(powf((a.x - b.x),2)+powf((a.y - b.y),2));
	return l;
}
float str(float x,float y,float z){
	float p = (x+y+z)/2;
	float str = sqrt(p*(p-x)*(p-y)*(p-z));
	return str;
}