public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = sc . nextInt ( ) ;
  int [ ] a = new int [ N ] ;
  int [ ] cnt = new int [ N ] ;
  int min = N + 1 ;
  int max = 0 ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    a [ i ] = sc . nextInt ( ) ;
    cnt [ a [ i ] ] += 1 ;
    min = Math . min ( min , a [ i ] ) ;
    max = Math . max ( max , a [ i ] ) ;
  }
  sc . close ( ) ;
  String POSSIBLE = "Possible" ;
  String IMPOSSIBLE = "Impossible" ;
  String ans = POSSIBLE ;
  if ( cnt [ min ] == 1 ) {
    if ( max == min * 2 ) {
      ans = POSSIBLE ;
      for ( int i = min + 1 ;
      i <= max ;
      i ++ ) {
        if ( cnt [ i ] < 2 ) {
          ans = IMPOSSIBLE ;
          break ;
        }
      }
    }
    else {
      ans = IMPOSSIBLE ;
    }
  }
  else if ( cnt [ min ] == 2 ) {
    if ( max == min * 2 - 1 ) {
      ans = POSSIBLE ;
      for ( int i = min + 1 ;
      i <= max ;
      i ++ ) {
        if ( cnt [ i ] < 2 ) {
          ans = IMPOSSIBLE ;
          break ;
        }
      }
    }
    else {
      ans = IMPOSSIBLE ;
    }
  }
  else {
    ans = IMPOSSIBLE ;
  }
  System . out . println ( ans ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = sc . nextInt ( ) ; int [ ] a = new int [ N ] ; int [ ] cnt = new int [ N ] ; int min = N + 1 ; int max = 0 ; for ( int i = 0 ; i < N ; i ++ ) { a [ i ] = sc . nextInt ( ) ; cnt [ a [ i ] ] += 1 ; min = Math . min ( min , a [ i ] ) ; max = Math . max ( max , a [ i ] ) ; } sc . close ( ) ; String POSSIBLE = " Possible " ; String IMPOSSIBLE = " Impossible " ; String ans = POSSIBLE ; if ( cnt [ min ] == 1 ) { if ( max == min * 2 ) { ans = POSSIBLE ; for ( int i = min + 1 ; i <= max ; i ++ ) { if ( cnt [ i ] < 2 ) { ans = IMPOSSIBLE ; break ; } } } else { ans = IMPOSSIBLE ; } } else if ( cnt [ min ] == 2 ) { if ( max == min * 2 - 1 ) { ans = POSSIBLE ; for ( int i = min + 1 ; i <= max ; i ++ ) { if ( cnt [ i ] < 2 ) { ans = IMPOSSIBLE ; break ; } } } else { ans = IMPOSSIBLE ; } } else { ans = IMPOSSIBLE ; } System . out . println ( ans ) ; }
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