public static void main ( String args [ ] ) {
  Scanner scan = new Scanner ( System . in ) ;
  int n = scan . nextInt ( ) ;
  long a [ ] = new long [ n ] ;
  for ( int index = 0 ;
  index < n ;
  index ++ ) {
    a [ index ] = scan . nextInt ( ) ;
  }
  long b [ ] = new long [ n ] , cnt = 0 ;
  for ( int index = 0 ;
  index < n ;
  index ++ ) {
    if ( a [ index ] == 0 ) cnt ++ ;
    b [ index ] = cnt ;
  }
  long sum = 0 ;
  for ( int index = n - 1 ;
  index >= 0 ;
  index -- ) {
    if ( a [ index ] != 0 ) sum += b [ n - 1 ] - b [ index ] ;
  }
  System . out . println ( sum ) ;
  return ;
}

public static void main ( String args [ ] ) { Scanner scan = new Scanner ( System . in ) ; int n = scan . nextInt ( ) ; long a [ ] = new long [ n ] ; for ( int index = 0 ; index < n ; index ++ ) { a [ index ] = scan . nextInt ( ) ; } long b [ ] = new long [ n ] , cnt = 0 ; for ( int index = 0 ; index < n ; index ++ ) { if ( a [ index ] == 0 ) cnt ++ ; b [ index ] = cnt ; } long sum = 0 ; for ( int index = n - 1 ; index >= 0 ; index -- ) { if ( a [ index ] != 0 ) sum += b [ n - 1 ] - b [ index ] ; } System . out . println ( sum ) ; return ; }
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