#define cross(a1, b1, a2, b2) ((a1)*(b2)-(a2)*(b1))
int main(){
  double a[50],b[50],s,t,x;
  int n,c=1,i;
  for(;scanf("%d",&n),n;printf("%d %.1lf\n",c,fabs(s-t)),c++){
    for(i=0;i<n;i++)scanf("%lf%lf",a+i,b+i);
    for(i=s=t=0;i<n-1;i++){
      if((x=cross(a[i],b[i],a[i+1],b[i+1]))>0)
        s+=fabs(x)/2.0;
      else
        t+=fabs(x)/2;
    }
    if((x=cross(a[i],b[i],a[0],b[0]))>0)
      s+=fabs(x)/2;
    else
      t+=fabs(x)/2;
  }
}