#include <stdio.h>
#include <math.h>

double area_tri ( double x0, double y0, double x1, double y1, double x2, double y2 ) {
	x1 -= x0;
	y1 -= y0;
	x2 -= x0;
	y2 -= y0;

	return fabs( ( x1 * y2 - y1 * x2 ) ) / 2.0;
}

int main( void ) {
	int i;
	int n;
	int a = 0;

	while ( scanf( "%d", &n ), n ) {
		double area = 0.0, x0, y0, x1, y1, x2, y2;

		scanf( "%lf %lf %lf %lf", &x0, &y0, &x1, &y1 );

		for ( i = 0; i < n - 2; i++ ) {
			scanf( "%lf %lf", &x2, &y2 );
			area += area_tri( x0, y0, x1, y1, x2, y2 );
			x1 = x2;
			y1 = y2;
		}

		printf( "%d %f\n", a++, area );
	}

	return 0;
}