#include <stdio.h>

int main(void){
	
	int n_polygon = 0,
		n, i,
		curX, curY, prevX, prevY, firstX, firstY;
	double s;
	
	while(1){
		
		scanf("%d", &n);
		if(n <= 0) break;
		
		s = 0;
		
		scanf("%d%d", &prevX, &prevY);
		firstX = prevX;
		firstY = prevY;
		for(i=0; i<n-1; i++){
			scanf("%d%d", &curX, &curY);
			s += (prevX - curX) * (prevY + curY);
			prevX = curX;
			prevY = curY;
		}
		s += (prevX - firstX) * (prevY + firstY);
		s /= 2;
		
		printf("%d %.1f\n", ++n_polygon, (s<0?-s:s));
		
	}
	
}