using System;
using System.Collections.Generic;
using System.Linq;

namespace Problem_04
{
    class Program
    {
        static void Main()
        {
            string[] inputElements = Console.ReadLine().Split(' ').ToArray();
            string tempStr = "";
            tempStr = inputElements[0];

            for (int i = 0; i < inputElements.Length; i++)
            {
                if (i < inputElements.Length-1)
                {
                    if (inputElements[i] == inputElements[i + 1])
                    {
                        if (tempStr == "")
                        {
                            tempStr = inputElements[i];
                        }

                        tempStr = tempStr + " " + inputElements[i + 1];

                        if (i == inputElements.Length-2)
                        {
                            Console.WriteLine(tempStr);
                        }
                    }
                    else
                    {
                        if (tempStr == "")
                        {
                            tempStr = inputElements[i];
                        }
                        Console.WriteLine(tempStr);
                        tempStr = "";
                    }
                }
                else
                {
                    if (inputElements.Length > 1 && (inputElements[inputElements.Length-1] != inputElements[inputElements.Length-2]))
                    {
                        tempStr = inputElements[inputElements.Length-1];
                        Console.WriteLine(tempStr);
                    }
                    else if (inputElements.Length == 1)
                    {
                        tempStr = inputElements[i];
                        Console.WriteLine(tempStr);
                    }
                }
            }
        }
    }
}