public static void main ( String args [ ] ) {
  FastScanner input = new FastScanner ( ) ;
  int n = input . nextInt ( ) ;
  HashMap < Long , Long > map = new HashMap < > ( ) ;
  long a [ ] = new long [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    a [ i ] = input . nextLong ( ) ;
    map . put ( i - a [ i ] , map . getOrDefault ( i - a [ i ] , 0L ) + a [ i ] ) ;
  }
  Long ans = Long . MIN_VALUE ;
  for ( Map . Entry < Long , Long > entry : map . entrySet ( ) ) {
    Long key = entry . getKey ( ) ;
    Long value = entry . getValue ( ) ;
    ans = Math . max ( ans , value ) ;
  }
  System . out . println ( ans ) ;
}

public static void main ( String args [ ] ) { FastScanner input = new FastScanner ( ) ; int n = input . nextInt ( ) ; HashMap < Long , Long > map = new HashMap < > ( ) ; long a [ ] = new long [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { a [ i ] = input . nextLong ( ) ; map . put ( i - a [ i ] , map . getOrDefault ( i - a [ i ] , 0L ) + a [ i ] ) ; } Long ans = Long . MIN_VALUE ; for ( Map . Entry < Long , Long > entry : map . entrySet ( ) ) { Long key = entry . getKey ( ) ; Long value = entry . getValue ( ) ; ans = Math . max ( ans , value ) ; } System . out . println ( ans ) ; }
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