#include<stdio.h>

typedef struct{
  int x;
  int y;
}point;
double dabs(double a){
  return a>0.0?a:-a;
}
int main(){
  int i,n,pc,a,b,c,d;
  point ps[100];
  double area;

  pc=1;
  do{
    scanf("%d",&n);
    if(!n) break;
    for(i=0;i<n;i++) scanf("%d %d",&(ps[i].x),&(ps[i].y));
    for(i=1,area=0.0;i<n-1;i++){
      a=ps[i].x-ps[0].x;
      b=ps[i].y-ps[0].y;
      c=ps[i+1].x-ps[0].x;
      d=ps[i+1].y-ps[0].y;
      area+=(double)(a*d-b*c)/2.0;
    }
    printf("%d %.1lf\n",pc++,dabs(area));
  }while(1);
  return 0;
}