import java.util.Scanner;
import java.util.Stack;

/**
   This calculator uses the reverse Polish notation.
*/
public class Calculator
{
   public static void main(String[] args)
   {
      Scanner in = new Scanner(System.in);
      Stack<Integer> results = new Stack<>();
      System.out.println("Enter one number or operator per line, Q to quit. ");
      boolean done = false;
      while (!done)
      {         
         String input = in.nextLine();

         // If the command is an operator, pop the arguments and push the result

         if (input.equals("+"))
         {
            results.push(results.pop() + results.pop());
         }
         else if (input.equals("-"))
         {
            Integer arg2 = results.pop();
            results.push(results.pop() - arg2);
         }
         else if (input.equals("*") || input.equals("x"))
         {
            results.push(results.pop() * results.pop());
         }
         else if (input.equals("/"))
         {
            Integer arg2 = results.pop();
            results.push(results.pop() / arg2);
         }
         else if (input.equals("Q") || input.equals("q"))
         {
            done = true;
         }
         else 
         {
            // Not an operator--push the input value
            
            results.push(Integer.parseInt(input));
         }
         System.out.println(results);
      }
   }
}
