public static void main ( String [ ] args ) throws IOException {
  FastScanner fs = new FastScanner ( ) ;
  PrintWriter out = new PrintWriter ( System . out ) ;
  int tt = 1 ;
  while ( tt -- > 0 ) {
    int n = fs . nextInt ( ) ;
    int [ ] a = fs . readArray ( n ) ;
    ruffleSort ( a ) ;
    int [ ] pos = new int [ N ] ;
    Arrays . fill ( pos , - 1 ) ;
    boolean [ ] done = new boolean [ N ] ;
    for ( int i = 0 ;
    i < n ;
    i ++ ) {
      pos [ a [ i ] ] = i ;
    }
    for ( int i = 1 ;
    i < N ;
    i ++ ) {
      if ( pos [ i ] == - 1 ) pos [ i ] = pos [ i - 1 ] ;
    }
    int ans = 0 ;
    for ( int i = 0 ;
    i < n ;
    i ++ ) {
      if ( ! done [ a [ i ] ] ) {
        done [ a [ i ] ] = true ;
        for ( int j = 2 * a [ i ] ;
        j < N ;
        j += a [ i ] ) {
          int ind = pos [ j - 1 ] ;
          if ( ind != i ) ans = Math . max ( ans , a [ ind ] % a [ i ] ) ;
          if ( ind == n - 1 ) break ;
        }
      }
    }
    out . println ( ans ) ;
  }
  out . close ( ) ;
}

public static void main ( String [ ] args ) throws IOException { FastScanner fs = new FastScanner ( ) ; PrintWriter out = new PrintWriter ( System . out ) ; int tt = 1 ; while ( tt -- > 0 ) { int n = fs . nextInt ( ) ; int [ ] a = fs . readArray ( n ) ; ruffleSort ( a ) ; int [ ] pos = new int [ N ] ; Arrays . fill ( pos , - 1 ) ; boolean [ ] done = new boolean [ N ] ; for ( int i = 0 ; i < n ; i ++ ) { pos [ a [ i ] ] = i ; } for ( int i = 1 ; i < N ; i ++ ) { if ( pos [ i ] == - 1 ) pos [ i ] = pos [ i - 1 ] ; } int ans = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( ! done [ a [ i ] ] ) { done [ a [ i ] ] = true ; for ( int j = 2 * a [ i ] ; j < N ; j += a [ i ] ) { int ind = pos [ j - 1 ] ; if ( ind != i ) ans = Math . max ( ans , a [ ind ] % a [ i ] ) ; if ( ind == n - 1 ) break ; } } } out . println ( ans ) ; } out . close ( ) ; }
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