public static void main ( String [ ] args ) throws Exception {
  InputStreamReader is = new InputStreamReader ( System . in ) ;
  BufferedReader br = new BufferedReader ( is ) ;
  String input [ ] = br . readLine ( ) . split ( " " ) ;
  int count = Integer . parseInt ( input [ 0 ] ) ;
  int maxLength = Integer . parseInt ( input [ 1 ] ) ;
  String input2 [ ] = br . readLine ( ) . split ( " " ) ;
  ArrayList < Integer > result = new ArrayList < Integer > ( ) ;
  for ( int i = 0 ;
  i < count ;
  i ++ ) {
    if ( i + 1 >= count ) {
      break ;
    }
    int num = Integer . parseInt ( input2 [ i ] ) ;
    int num2 = Integer . parseInt ( input2 [ i + 1 ] ) ;
    if ( num + num2 >= maxLength ) {
      for ( int j = 0 ;
      j < i ;
      j ++ ) {
        result . add ( j + 1 ) ;
      }
      for ( int n = count - 1 ;
      n > i + 1 ;
      n -- ) {
        result . add ( n ) ;
      }
      result . add ( i + 1 ) ;
      System . out . println ( "Possible" ) ;
      for ( int re : result ) {
        System . out . println ( re ) ;
      }
      return ;
    }
  }
  System . out . println ( "Impossible" ) ;
}

public static void main ( String [ ] args ) throws Exception { InputStreamReader is = new InputStreamReader ( System . in ) ; BufferedReader br = new BufferedReader ( is ) ; String input [ ] = br . readLine ( ) . split ( " ▁ " ) ; int count = Integer . parseInt ( input [ 0 ] ) ; int maxLength = Integer . parseInt ( input [ 1 ] ) ; String input2 [ ] = br . readLine ( ) . split ( " ▁ " ) ; ArrayList < Integer > result = new ArrayList < Integer > ( ) ; for ( int i = 0 ; i < count ; i ++ ) { if ( i + 1 >= count ) { break ; } int num = Integer . parseInt ( input2 [ i ] ) ; int num2 = Integer . parseInt ( input2 [ i + 1 ] ) ; if ( num + num2 >= maxLength ) { for ( int j = 0 ; j < i ; j ++ ) { result . add ( j + 1 ) ; } for ( int n = count - 1 ; n > i + 1 ; n -- ) { result . add ( n ) ; } result . add ( i + 1 ) ; System . out . println ( " Possible " ) ; for ( int re : result ) { System . out . println ( re ) ; } return ; } } System . out . println ( " Impossible " ) ; }
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