class ListElement
{
	private int data; // the actual data in the list element
	private ListElement next; // reference of the next element in the list
	
	public ListElement(int dat) //this constructor will set next to null - so only use for end of list
	{
		data = dat; // given parameter value
		next = null; // default
	}
	public ListElement(int dat, ListElement after)
	{	
		data = dat; // given parameter value
		next = after; // given parameter value
	}
		
	public ListElement next(){
		return next;
	}
	
	public void setNext(ListElement new_next){
		next = new_next;
	}
	
	public int getData(){
		return data;
	}
	
	public String toString() // overwrite toString() for easy printing
	{
		return " -> "+data+" -> "; 
	}	
}



class FiFoList
{
	private ListElement first; // reference of the first element
	private ListElement last; // reference of the last element (aids fast adding)
	
	public FiFoList()
	{	
		first = null; //
		last = first; // indicates an empty list (both first and last are null)
	}
		
	//pre: -
	//post: return a string that is simply the concatenation of calling 
	//		the toString method of all list elements.
	//		make sure that you print in "youngest" to "oldest" order	
	public String toString() 
	{	
		ListElement le = first; // starting point
		String str = "";
		while (le != null)
		{			
			str += le.toString(); // adds the Strings
			le = le.next(); // go from one element to the next one
		}
		return str;
	}
	
	//pre: the list with m elements, where m can be any positive integer including 0 (empty list)
	//post: the list with m+1 elements, with one element added by you (ListElement with data "n")
	//		you can choose on which side you add the element, as long you remove from the other and traverse correctly
	//		when printing
	public void insert(int n)
	{	
		ListElement le = new ListElement(n,null); // create new element
		if (last == null){ //this assumes that both have to null at the same time always
			first = le;
			last = le;
		}
		else {
			last.setNext(le);
			last = le;
		}		
	}
	
	
	
	//pre: the list with m elements, where m can be any positive integer including 0 (empty list)
	//post: if the list is empty return 0 and leave the list empty,
	//		otherwise return the "data" value of the oldest element and remove it from the list
	public int remove()
	{
		if(first == null)
		{
			return 0;
		}
		else {
			ListElement le = first;
			if (last == first) // in case we only have one element
			{
				first = last = le.next();
			}
			else {
				first = le.next();
			}
			return le.getData();
		}		
	}	
}


//---------------------------------------------------------------------------------
// Unfortunately it is a restriction of the judge that we always have to have a public class Main in our file
// The code below is only used to validate your code with the judge - feel free to browse - but its not required for the exercise
//------------------------------------------------------------------------------------------------------------------------
class Main{
	public static void main(String[] args) {
		java.util.Scanner scanner = new java.util.Scanner(System.in);
				
		FiFoList fifolist = new FiFoList();		
		String str = "";
		String pop = "";
		while(scanner.hasNextInt()){
			int insert_or_remove = scanner.nextInt();			
			if (insert_or_remove > 0){
				fifolist.insert(insert_or_remove);
				pop = "";
			}
			else
				pop = " pop: " + fifolist.remove();
			str += fifolist.toString();
			str += pop + "\n";
		  }
		scanner.close();
		System.out.println(str);
	  }
	}

/*
 You can test your implementation of Insert and toString with the following input:
1
2
3
4
5
6
7
8
9
end


This should give you the following output
 -> 1 -> 
 -> 1 ->  -> 2 -> 
 -> 1 ->  -> 2 ->  -> 3 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 ->  -> 5 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 ->  -> 5 ->  -> 6 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 ->  -> 5 ->  -> 6 ->  -> 7 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 ->  -> 5 ->  -> 6 ->  -> 7 ->  -> 8 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 ->  -> 5 ->  -> 6 ->  -> 7 ->  -> 8 ->  -> 9 -> 
  
  
  To also test the remove function you can use the following input
  
  1
2
-3
4
-8
-8
-9
2
1
-4
-4
1
2
3
4
5
6
-1
-1
-1
99
end

Which should give you the following output:

  -> 1 -> 
 -> 1 ->  -> 2 -> 
 -> 2 ->  pop: 1
 -> 2 ->  -> 4 -> 
 -> 4 ->  pop: 2
 pop: 4
 pop: 0
 -> 2 -> 
 -> 2 ->  -> 1 -> 
 -> 1 ->  pop: 2
 pop: 1
 -> 1 -> 
 -> 1 ->  -> 2 -> 
 -> 1 ->  -> 2 ->  -> 3 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 ->  -> 5 -> 
 -> 1 ->  -> 2 ->  -> 3 ->  -> 4 ->  -> 5 ->  -> 6 -> 
 -> 2 ->  -> 3 ->  -> 4 ->  -> 5 ->  -> 6 ->  pop: 1
 -> 3 ->  -> 4 ->  -> 5 ->  -> 6 ->  pop: 2
 -> 4 ->  -> 5 ->  -> 6 ->  pop: 3
 -> 4 ->  -> 5 ->  -> 6 ->  -> 99 -> 
  
 */