typedef struct{
	double x,y;
}point;

double shoelace(char* inputFile){
	int i,numPoints;
	double leftSum = 0,rightSum = 0;

	point* pointSet;
	FILE* fp = fopen(inputFile,);

	fscanf(fp,,&numPoints);

	pointSet = (point*)malloc((numPoints + 1)*sizeof(point));

	for(i=0;i<numPoints;i++){
		fscanf(fp,,&pointSet[i].x,&pointSet[i].y);
	}

	fclose(fp);

	pointSet[numPoints] = pointSet[0];

	for(i=0;i<numPoints;i++){
		leftSum += pointSet[i].x*pointSet[i+1].y;
		rightSum += pointSet[i+1].x*pointSet[i].y;
	}

	free(pointSet);

	return 0.5*fabs(leftSum - rightSum);
}

int main(int argC,char* argV[])
{
	if(argC==1)
		printf(,argV[0]);

	else
		printf(,shoelace(argV[1]));

	return 0;
}