public struct Tovar
        {
            public string Number;
            public string SerialCode;
            public string Sklad;
        }

        static void Main(string[] args)
        {
            var Data = new List<string>() { @"N101" + "\n" + @"Серийник:12345" + "\n" + @"N203" + "\n" + @"Серийник:67890" + "\n" + @"N203" + "\n" + @"Склад:1" + "\n" + @"N101" + "\n" + @"Склад:3" };
            Data.Add(@"N201" + "\n" + @"Серийник:22345" + "\n" + @"N303" + "\n" + @"Серийник:77890" + "\n" + @"N303" + "\n" + @"Склад:2" + "\n" + @"N201" + "\n" + @"Склад:4");
            var tovar = new List<Tovar>();
            Tovar _tov = new Tovar();
            int i = 1;

            var Response = Data.Select(x => x);

            foreach (string res in Response)
            {
                string[] arr = res.Split('\n');
                foreach (string s in arr)
                {
                    if (s.IndexOf("N") != -1)
                    {
                        _tov.Number = s;
                    }
                    else if (s.IndexOf("Серийник") != -1)
                    {
                        _tov.SerialCode = s;
                        _tov.Sklad = string.Empty;
                    }
                    else
                    {
                        _tov.Sklad = s;
                        _tov.SerialCode = string.Empty;
                    }

                    if (i == 2)
                    {
                        tovar.Add(_tov);
                        i = 0;
                    }
                    i++;
                }
            }

            foreach (var row in tovar)
            {
                Console.WriteLine(row.Number + " Sklad or Serial: " + row.Sklad + row.SerialCode);
            }

            Console.ReadKey();
        }
    }

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