import java.util.Iterator;
import java.util.NoSuchElementException;


public class Ochered implements Iterable<Student> {

        private Student[] q;
        private int head;
        private static Ochered o;

        private Ochered(int n) {
            q = new Student[n+1];
            head = -1;
        }

        public static Ochered getInstance(int n) {

            if (o == null) {
                return o = new Ochered(n);
            }
            else return o;
        }

        public boolean isEmpty(){
            if (head == -1)
                return true;
            else return false;
        }

        public void push(Student stud) throws Exception{
            if (head == q.length-1) throw new Exception("Overflow");
            head++;
            q[head] = stud;
        }

        public Student peek() throws Exception{
            if (isEmpty()) throw new Exception("Underflow");

            return q[0];
        }

        public Student pop() throws Exception{
             if (head == -1) throw new Exception("Underflow");

                Student tmp = q[0];

                for (int i = 0; i < head; i ++) {
                 q[i] = q[i+1];
                }

                q[head] = null;
                head--;


             return tmp;

        }

        public Iterator<Student> iterator() {
              return new Iterator<Student>() {
                int i = 0;
                Student next = q[0];
                public boolean hasNext() {
                    return next != null;
                }
                public Student next() {
                    if (i > head) throw new NoSuchElementException();
                    Student current = next;
                    i++;
                    next = q[i];
                    return current;
                }
                public void remove() {
                    throw new UnsupportedOperationException();
                }
              };
            }



}