public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int stonesNum ;
  int gifts ;
  stonesNum = sc . nextInt ( ) ;
  gifts = ( stonesNum / 3 ) * 2 ;
  if ( stonesNum % 3 > 0 ) gifts ++ ;
  System . out . println ( gifts ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int stonesNum ; int gifts ; stonesNum = sc . nextInt ( ) ; gifts = ( stonesNum / 3 ) * 2 ; if ( stonesNum % 3 > 0 ) gifts ++ ; System . out . println ( gifts ) ; }
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