public static void main ( String [ ] args ) {
  MathContext mc = new MathContext ( 25 , RoundingMode . HALF_DOWN ) ;
  Scanner in = new Scanner ( System . in ) ;
  int n = in . nextInt ( ) ;
  int a = in . nextInt ( ) ;
  int x = in . nextInt ( ) ;
  BigDecimal L = new BigDecimal ( 1 ) ;
  BigDecimal ans = new BigDecimal ( 2 * x ) ;
  for ( int i = 2 ;
  i <= n ;
  ++ i ) {
    BigDecimal t = new BigDecimal ( i ) ;
    L = L . add ( BigDecimal . ONE . divide ( BigDecimal . valueOf ( i ) , mc ) ) ;
    t = L . add ( BigDecimal . valueOf ( i ) ) ;
    t = t . multiply ( BigDecimal . valueOf ( x ) ) ;
    BigDecimal t2 = ans . multiply ( BigDecimal . valueOf ( 2 ) ) . divide ( BigDecimal . valueOf ( i ) , mc ) ;
    ans = ans . add ( t ) . add ( t2 ) ;
  }
  L = L . add ( BigDecimal . ONE . divide ( BigDecimal . valueOf ( n + 1 ) , mc ) ) ;
  L = L . subtract ( BigDecimal . ONE ) ;
  L = L . multiply ( BigDecimal . valueOf ( n + 1 ) ) . multiply ( BigDecimal . valueOf ( 2 * a - 3 * x ) ) ;
  L = L . divide ( BigDecimal . valueOf ( 2 ) , mc ) ;
  ans = ans . add ( L ) ;
  System . out . print ( ans ) ;
}

public static void main ( String [ ] args ) { MathContext mc = new MathContext ( 25 , RoundingMode . HALF_DOWN ) ; Scanner in = new Scanner ( System . in ) ; int n = in . nextInt ( ) ; int a = in . nextInt ( ) ; int x = in . nextInt ( ) ; BigDecimal L = new BigDecimal ( 1 ) ; BigDecimal ans = new BigDecimal ( 2 * x ) ; for ( int i = 2 ; i <= n ; ++ i ) { BigDecimal t = new BigDecimal ( i ) ; L = L . add ( BigDecimal . ONE . divide ( BigDecimal . valueOf ( i ) , mc ) ) ; t = L . add ( BigDecimal . valueOf ( i ) ) ; t = t . multiply ( BigDecimal . valueOf ( x ) ) ; BigDecimal t2 = ans . multiply ( BigDecimal . valueOf ( 2 ) ) . divide ( BigDecimal . valueOf ( i ) , mc ) ; ans = ans . add ( t ) . add ( t2 ) ; } L = L . add ( BigDecimal . ONE . divide ( BigDecimal . valueOf ( n + 1 ) , mc ) ) ; L = L . subtract ( BigDecimal . ONE ) ; L = L . multiply ( BigDecimal . valueOf ( n + 1 ) ) . multiply ( BigDecimal . valueOf ( 2 * a - 3 * x ) ) ; L = L . divide ( BigDecimal . valueOf ( 2 ) , mc ) ; ans = ans . add ( L ) ; System . out . print ( ans ) ; }
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