using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var str = "N1N2S3S4L5L6O7O8X";

        var lista = SemLinq(str);       

        foreach (var kvp in lista)

        {

            Console.WriteLine($"Key: {kvp.Key} Value: {kvp.Value}");

        }

        var lista2 = ComLinq(str);

        foreach (var kvp in lista)

        {

            Console.WriteLine($"Key: {kvp.Key} Value: {kvp.Value}");

        }

    }

    public static List<KeyValuePair<char, char>> ComLinq(string str)

    {

        var lista = str.Zip(str.Skip(1), (k, v) => new KeyValuePair<char, char>(k, v)).Where((pair, index) => index % 2 == 0);

        foreach (var kvp in lista)

        {

            Console.WriteLine($"Key: {kvp.Key} Value: {kvp.Value}");

        }

        return lista.ToList();

    }

    public static List<KeyValuePair<char, char>> SemLinq(string str)

    {

        var lista = new List<KeyValuePair<char, char>>();

        for(int i = 0; i < str.Length - 1; i += 2)

        {

            lista.Add(new KeyValuePair<char, char>(str[i], str[i + 1]));

        }

        return lista;       

    }

}