public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  Double x1 = sc . nextDouble ( ) ;
  Double y1 = sc . nextDouble ( ) ;
  Double x2 = sc . nextDouble ( ) ;
  Double y2 = sc . nextDouble ( ) ;
  Double x3 = sc . nextDouble ( ) ;
  Double y3 = sc . nextDouble ( ) ;
  x3 -= x1 ;
  y3 -= y1 ;
  x2 -= x1 ;
  y2 -= y1 ;
  x1 -= x1 ;
  y1 -= y1 ;
  System . out . println ( Math . abs ( ( x3 * y2 ) - x2 * y3 ) / 2 ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; Double x1 = sc . nextDouble ( ) ; Double y1 = sc . nextDouble ( ) ; Double x2 = sc . nextDouble ( ) ; Double y2 = sc . nextDouble ( ) ; Double x3 = sc . nextDouble ( ) ; Double y3 = sc . nextDouble ( ) ; x3 -= x1 ; y3 -= y1 ; x2 -= x1 ; y2 -= y1 ; x1 -= x1 ; y1 -= y1 ; System . out . println ( Math . abs ( ( x3 * y2 ) - x2 * y3 ) / 2 ) ; }
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