public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = sc . nextInt ( ) ;
  double d1 = sc . nextInt ( ) ;
  double x = sc . nextInt ( ) ;
  double ans = 0 ;
  for ( ;
  N > 0 ;
  N -- ) {
    ans += d1 + ( N - 0.5 ) * x ;
    d1 = ( ( 2 * N + 2 ) * d1 + 5 * x ) / ( 2 * N ) ;
    x = ( ( double ) N + 2 ) / N * x ;
  }
  System . out . println ( ans ) ;
  sc . close ( ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = sc . nextInt ( ) ; double d1 = sc . nextInt ( ) ; double x = sc . nextInt ( ) ; double ans = 0 ; for ( ; N > 0 ; N -- ) { ans += d1 + ( N - 0.5 ) * x ; d1 = ( ( 2 * N + 2 ) * d1 + 5 * x ) / ( 2 * N ) ; x = ( ( double ) N + 2 ) / N * x ; } System . out . println ( ans ) ; sc . close ( ) ; }
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