//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string awal = "qwertyuioplkjhgfdsazxcvbnm";
            char[] awalChars = awal.ToCharArray();
            string hasil = "";
            string kal = "aD4_3an9X-B15a+13@#4_!Ni3eE?!?!";
            char[] kalChar = kal.ToCharArray();

            for (int i = 0; i < kal.Length; i++){
                if (awal.IndexOf(kalChar[i]) > 0){
                    hasil = hasil + kalChar[i];
                }
            }
            //Your code goes here
            Console.WriteLine(hasil);
        }
    }
}