using System;

using System.Threading.Tasks;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var dictionary = new Dictionary<int, int>();

        var task1 = Task.Run(() => {

            for (int i = 0; i < 100; i++)

            {

                dictionary.Add(i, i + 1);

            }

        });

​

        var task2 = Task.Run(() => {

            for (int i = 0; i < 100; i++)

            {

                dictionary.Add(i + 1, i);

            }

        });

​

        Task[] allTasks = { task1, task2 };

        Task.WaitAll(allTasks);

    }

}