public static void main ( String args [ ] ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] arr = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    arr [ i ] = sc . nextInt ( ) ;
  }
  int a = 0 , b = 0 , temp = 0 , c = 0 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( arr [ i ] == 1 ) a ++ ;
    else break ;
  }
  for ( int i = n - 1 ;
  i >= 0 ;
  i -- ) {
    if ( arr [ i ] == 1 ) b ++ ;
    else break ;
  }
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    if ( arr [ i ] == 1 ) c ++ ;
    else c = 0 ;
    temp = Math . max ( temp , c ) ;
  }
  System . out . println ( Math . max ( temp , a + b ) ) ;
}

public static void main ( String args [ ] ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] arr = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { arr [ i ] = sc . nextInt ( ) ; } int a = 0 , b = 0 , temp = 0 , c = 0 ; for ( int i = 0 ; i < n ; i ++ ) { if ( arr [ i ] == 1 ) a ++ ; else break ; } for ( int i = n - 1 ; i >= 0 ; i -- ) { if ( arr [ i ] == 1 ) b ++ ; else break ; } for ( int i = 0 ; i < n ; i ++ ) { if ( arr [ i ] == 1 ) c ++ ; else c = 0 ; temp = Math . max ( temp , c ) ; } System . out . println ( Math . max ( temp , a + b ) ) ; }
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