using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var query = new Span<char>("instanceId=123asdasd&a=v&asd=123&instanceId=123".ToArray());

        var instanceId = "instanceId=".ToArray();

        var total = 0;

        var expected = 0;

        for(var i = 0; i < query.Length; i++)

        {

            if(query[i]== instanceId[expected])

            {

                query[total] = instanceId[expected];

                expected++;

                total++;

                if(expected == instanceId.Length)

                {

                    do

                    {

                        i++;

                        if(i ==  query.Length)

                        {

                            break;

                        }else

                        {

                            query[total] = query[i];

                            total++;

                            if(query[i] == '&'){

                                expected = 0;

                                break;

                            }

                        }

                    }while(true);

                }

            }else

                {

                    total = total - expected;

                    expected = 0;

                }

        }

        Console.WriteLine(query[..total].ToString());

    }

}