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

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {
            // data variables
            string username = "john";
            string password = "doe";
            // keyboard input
            string user = "";
            string pass = "";

            do {

                Console.WriteLine("Please enter username:");
                user = Console.ReadLine();
                Console.WriteLine("Please enter password:");
                pass = Console.ReadLine();

                if (user == username) {
                    if (pass == password)
                    {
                        Console.WriteLine("Welcome to our system!");

                    }
                    else
                    {
                        Console.WriteLine("Invalid password");
                    }
                }
                else
                {
                    Console.WriteLine("No such user found!");
                }
            } while (username != user || password != pass);


            Console.ReadKey();
        }
    }
}