poj 2954

#include<stdio.h>

#include<math.h>
struct Point
{
	int x,y;
}point[5];

int gcd(int a,int b)
{
	if(b==0) 
		return a;
	return gcd(b,a%b);
}
int Onside()
{
    int i,ret=0;
	for(i=0;i<3;i++)
		ret+=gcd(abs(point[i].x-point[(i+1)%3].x),abs(point[i].y-point[(i+1)%3].y));
	return ret;
}

double aarea()
{
	int i,sum=0;
	
	for(i=0;i<3;i++)
	{
	    sum+=point[(i+1)%3].y*(point[i].x-point[(i+2)%3].x);
	}
	return abs(1.0*sum/2);
}

int main()
{
	int area,onside;
	while(scanf("%d%d%d%d%d%d",&point[0].x,&point[0].y,&point[1].x,&point[1].y,&point[2].x,&point[2].y))
	{
		if(point[0].x==0 && point[0].y==0 && point[1].x==0 && point[1].y==0 && point[2].x==0 && point[2].y==0)
			break;
		area=(int)aarea();
		onside=Onside();
		printf("%d\n",(area+1)-onside/2);
	}
	return 0;
}