text: #define cross(a1, b1, a2, b2) ((a1)*(b2)-(a2)*(b1))
  main(){
  	double a[100],b[100],s,t,x;
  	int n,c=1,i;
  	for(;scanf("%d",&n),n;printf("%d %.1lf\n",c,fabs(s-t)),c++){ // for(;~scanf("%d",&n);printf("%.1lf\n",fabs(s-t))) for CGL~3A
  		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;
  			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;
  	}
  exit(0);}