#include <stdio.h>

#define ABS(X) \
  ( (X) < 0 ? -(X) : (X) )

/** Application main entry point. */
int
main (
  int     argc,
  char  * argv[ ]
  )
{
  int sqn;

  for ( sqn = 1; ; ++sqn )
  {
    double res = 0.;
    int ox, oy;
    int px, py;
    int n;

    scanf ( "%d", &n );
    if ( !( n ) ) break ;

    scanf ( "%d%d", &ox, &oy );
    px = ox; py = oy;
    while ( n-- )
    {
      int x, y;
      
      if ( n )
      {
        scanf ( "%d%d", &x, &y );
      }
      else
      {
        x = ox; y = oy;
      }

      res += ( ( ( px - ox ) - ( x - ox ) )
             * ( ( py - oy ) + ( y - oy ) ) ) / 2.;

      px = x; py = y;
    }

    printf ( "%d %.1f\n", sqn, ABS( res ) );
  }

  return ( 0 );
}