public class Evaluate

{

    public static void main(String[] args)

    {

        Stack<String> ops=new Stack<String>();

        Stack<Double> vals=new Stack<Double>();

        while(!StdIn.isEmpty())

        {//标识符是运算符时压入运算符栈

            String s=StdIn.readString();

            if        (s.equals("("));

            else if (s.equals("+"))  ops.push(s);

            else if (s.equals("-")) ops.push(s);

            else if (s.equals("*")) ops.push(s);

            else if (s.equals("/")) ops.push(s);

            else if (s.equals("sqrt")) ops.push(s);

            else if (s.equals(")"))

             {//标识符为右括号时，弹出运算符和适当数量的操作数，计算结果压入操作数栈，注意第一次先弹出的操作数在运算时应在运算符的左边。

                String op=ops.pop();

                double v=vals.pop();

                if (op.equals("+")) v=vals.pop()+v;

                else if (op.equals("-"))  v=vals.pop()-v;

                else if (op.equals("*"))  v=vals.pop()*v;

                else if (op.equals("/"))  v=vals.pop()/v;

                else if (op.equals("sqrt")) v=Math.sqrt(v);

                vals.push(v);

            }

        //即不是运算符也不是括号时，将其作为double型值压入操作数栈

            else vals.push(Double.parseDouble(s));

        }//end while

         StdOut.println(vals.pop());

    }//end main

}//end class