#include <stdio.h>
int main(void){
    int px[50],py[50],np,i,sign,cnt = 1;
    double area;
    scanf("%d", &np);
    while( np > 0 ){
        for(i = 0; i < np; i++){
            scanf( "%d %d", &px[i], &py[i] );
        }
        area = 0;
        for(i = 2; i < np; i++){
            area += (double)( (px[i] - px[0])*(py[i-1] - py[0])
                              - (px[i-1] - px[0])*(py[i] - py[0]) )/2;

        }
        printf("%d %.1lf\n",cnt++, area);
        scanf("%d", &np);
    }
    return 0;
}