public static void main ( String [ ] args ) {
  Scanner in = new Scanner ( System . in ) ;
  while ( in . hasNext ( ) ) {
    int n = in . nextInt ( ) ;
    long arr [ ] = new long [ 100005 ] ;
    long b [ ] = new long [ 100005 ] ;
    for ( int i = 0 ;
    i < n ;
    i ++ ) {
      arr [ i ] = in . nextInt ( ) ;
      b [ i ] = 1 ;
    }
    int j = 0 ;
    for ( int i = 1 ;
    i < n ;
    i ++ ) {
      if ( arr [ i ] == arr [ i - 1 ] ) {
        b [ j ] ++ ;
      }
      else {
        j ++ ;
      }
    }
    long sum = 0 ;
    for ( int i = 1 ;
    i <= j ;
    i ++ ) {
      sum = Math . max ( sum , Math . min ( b [ i ] , b [ i - 1 ] ) ) ;
    }
    System . out . println ( sum * 2 ) ;
  }
}

public static void main ( String [ ] args ) { Scanner in = new Scanner ( System . in ) ; while ( in . hasNext ( ) ) { int n = in . nextInt ( ) ; long arr [ ] = new long [ 100005 ] ; long b [ ] = new long [ 100005 ] ; for ( int i = 0 ; i < n ; i ++ ) { arr [ i ] = in . nextInt ( ) ; b [ i ] = 1 ; } int j = 0 ; for ( int i = 1 ; i < n ; i ++ ) { if ( arr [ i ] == arr [ i - 1 ] ) { b [ j ] ++ ; } else { j ++ ; } } long sum = 0 ; for ( int i = 1 ; i <= j ; i ++ ) { sum = Math . max ( sum , Math . min ( b [ i ] , b [ i - 1 ] ) ) ; } System . out . println ( sum * 2 ) ; } }
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