namespace _04.RecoverMessage
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;

internal class Node : IComparable
    {
        public Node()
        {
            this.Children = new HashSet<Node>();
        }

        public char Value { get; set; }

        public bool HasParent { get; set; }

        public double Weight { get; set; }

        public ICollection<Node> Children { get; set; }

        public int CompareTo(object obj)
        {
            return this.Value.CompareTo((obj as Node).Value);
        }

        public override int GetHashCode()
        {
            return this.Value.GetHashCode();
        }

        public override bool Equals(object obj)
        {
            return this.Value.Equals((obj as Node).Value);
        }
    }

    internal class Program
    {
        internal static void Main()
        {
            var n = int.Parse(Console.ReadLine());
            string[] messages = new string[n];
            var graph = BuildGraph(messages);
            var recoveredMessage = RecoverMessage(graph);
            Console.WriteLine(recoveredMessage);
        }

        private static string RecoverMessage(List<Node> graph)
        {
            var recoveredMessage = new StringBuilder();

            while (graph.Count > 0)
            {
                var root = graph.Where(node => node.HasParent == false).OrderBy(node => node.Value).First();
                recoveredMessage.Append(root.Value);
                graph.Remove(root);

                foreach (var child in root.Children)
                {
                    if (!graph.Any(node => node.Children.Any(c => c == child)))
                    {
                        child.HasParent = false;
                    }
                }
            }

            return recoveredMessage.ToString();
        }

        private static List<Node> BuildGraph(string[] messages)
        {
            var letters = new HashSet<Node>();
            for (int i = 0; i < messages.Length; i++)
            {
                messages[i] = Console.ReadLine();
                for (int j = 0; j < messages[i].Length; j++)
                {
                    letters.Add(new Node() { Value = messages[i][j] });
                }
            }

            var graph = letters.ToList();
            for (int i = 0; i < messages.Length; i++)
            {
                for (int j = 0; j < messages[i].Length; j++)
                {
                    var index = Array.IndexOf(graph.Select(g => g.Value).ToArray(), messages[i][j]);
                    if (j < messages[i].Length - 1)
                    {
                        var childNode = new Node() { Value = messages[i][j + 1] };
                        var childIndex = Array.IndexOf(graph.ToArray(), childNode);
                        graph[childIndex].HasParent = true;
                        graph[index].Children.Add(graph[childIndex]);
                    }
                }
            }

            return graph;
        }
    }
}