using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        Dictionary<int, string>[] matrix = new Dictionary<int, string>[2];

        matrix[0] = new Dictionary<int, string>();

        matrix[0].Add(0, "0");

        matrix[0].Add(1, "1");

        matrix[1] = new Dictionary<int, string>();

        matrix[1].Add(2, "2");

        IEnumerable<int> result = matrix.SelectMany(x => x.Keys);

        foreach (int i in result)

            Console.WriteLine(i);

    }

}