using System;

public class Program

{

    public static void Main()

    {

        string input="goodfellow";

        int[] f=new int[256];

        for(int i=0;i<input.Length;i++)

        {

            f[input[i]]++;

        }

        Console.WriteLine("Duplicate Characters in a given string is:");

        for(int i=0;i<input.Length;i++)

        {

            if(f[input[i]]>1)

            {

                Console.WriteLine(input[i]);

            }

        }       

    }

}