using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder
{
    public class Prog
    {
        const int MOD = 1000000007;
        public static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            new Prog().Solve(new ConsoleInput(Console.In, ' '));
            Console.Out.Flush();
        }

        public void Solve(ConsoleInput cin)
        {
            var n = cin.ReadInt;
            var s = cin.ReadStrArray(n);

            var dicl = new List<Dictionary<char, int>>();

            foreach (var str in s)
            {
                var dic = new Dictionary<char, int>();
                foreach (var c in str)
                {
                    if (dic.ContainsKey(c))
                    {
                        dic[c]++;
                    }
                    else
                    {
                        dic.Add(c, 1);
                    }
                }
                dicl.Add(dic);
            }

            var ans = string.Empty;

            foreach (var key in "abcdefghijklmnopqrstuvwxyz")
            {
                var min = int.MaxValue;
                foreach (var dic in dicl)
                {
                    if (dic.ContainsKey(key))
                    {
                        if (dic[key] < min)
                        {
                            min = dic[key];
                        }
                    }
                    else
                    {
                        min = 0;
                        break;
                    }
                }
                ans += new string(key, min);
            }

            Console.WriteLine(ans);
        }
    }
    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        public void ReadIntArrays(long N, out int[] A, out int[] B) { A = new int[N]; B = new int[N]; for (long i = 0; i < N; ++i) { A[i] = ReadInt; B[i] = ReadInt; } }
    }
}


Measured memory_bytes: 13408