using System;

using System.Text;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        PrintStringDuplicates("sasyuiuasaqwq");     

    }

    public static void PrintStringDuplicates(string input){

        var r = GetCharDictionary(input);

        var rs = new StringBuilder();

        foreach(var a in r){

            if(a.Value == 2){

                rs.Append(a.Key + " ");

            }

        }

        Console.WriteLine("Duplicates: " + rs.ToString());

    }

    public static Dictionary<string, int>  GetCharDictionary(string input){

        var charArray = input.ToCharArray();

        Dictionary<string, int> r = new Dictionary<string, int>();

        foreach(var a in charArray){

            if(r.ContainsKey(a.ToString())){

                r[a.ToString()] += 1;

            }else{

                r[a.ToString()] = 1;                

            }

        }

        return r;

    }

}