public class Stack {

	private Node head;
	public  Node next;

	public Stack() {
	    head = new Node();
	    head.data = 0;
	}
	public Stack( int d ) {
	    head = new Node();
	    head.data = d;
	}

	public int pop() {
		int temp;

		temp = head.data;
		head = head.next;

		return temp;
	}

	public void push( int d ) {
		Node tmp = new Node();
		tmp.data = d;
		tmp.next = head;
		head = tmp;
	}

	public int peek() {
		return head.data;
	}

    //Private Class
	private class Node{
		int data;
		Node next;
	}
}