abstract class Expr { 
  def eval: Int 
  def printExpr
} 

class Number(n: Int) extends Expr { 
  def eval: Int = n 
  def printExpr { print(n) }
}
 
class Sum(e1: Expr, e2: Expr) extends Expr { 
  def eval: Int = e1.eval + e2.eval 
  def printExpr { print("(") ; e1.printExpr ; print("+") ; e2.printExpr ; print(")") }
} 

class Prod(e1: Expr, e2: Expr) extends Expr { 
  def eval: Int = e1.eval * e2.eval 
  def printExpr { print("(") ; e1.printExpr ; print("*") ; e2.printExpr ; print(")") }
}