// stackTriangle2.java
// evaluates triangular numbers, stack replaces recursion
// to run this program: C>java StackTriangle2App
import java.io.*;                 // for I/O
////////////////////////////////////////////////////////////////
class StackX
   {
   private int maxSize;        // size of stack array
   private int[] stackArray;
   private int top;            // top of stack
//--------------------------------------------------------------
   public StackX(int s)        // constructor
      {
      maxSize = s;
      stackArray = new int[maxSize];
      top = -1;
      }
//--------------------------------------------------------------
   public void push(int p)     // put item on top of stack
      { stackArray[++top] = p; }
//--------------------------------------------------------------
   public int pop()            // take item from top of stack
      { return stackArray[top--]; }
//--------------------------------------------------------------
   public int peek()           // peek at top of stack
      { return stackArray[top]; }
//--------------------------------------------------------------
   public boolean isEmpty()    // true if stack is empty
      { return (top == -1); }
//--------------------------------------------------------------
   }  // end class StackX
////////////////////////////////////////////////////////////////
class StackTriangle2App
   {
   static int theNumber;
   static int theAnswer;
   static StackX theStack;

   public static void main(String[] args) throws IOException
      {
      System.out.print("Enter a number: ");
      System.out.flush();
      theNumber = getInt();
      stackTriangle();
      System.out.println("Triangle="+theAnswer);
      }  // end main()
//-------------------------------------------------------------
   public static void stackTriangle()
      {
      theStack = new StackX(10000);    // make a stack

      theAnswer = 0;                   // initialize answer

      while(theNumber > 0)             // until n is 1,
         {
         theStack.push(theNumber);     // push value
         --theNumber;                  // decrement value
         }
      while( !theStack.isEmpty() )     // until stack empty,
         {
         int newN = theStack.pop();    // pop value,
         theAnswer += newN;            // add to answer
         }
      }
//-------------------------------------------------------------
   public static String getString() throws IOException
      {
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader br = new BufferedReader(isr);
      String s = br.readLine();
      return s;
      }
//-------------------------------------------------------------
   public static int getInt() throws IOException
      {
      String s = getString();
      return Integer.parseInt(s);
      }
//--------------------------------------------------------------
   }  // end class StackTriangle2App
////////////////////////////////////////////////////////////////