public static void SplitTeamsByGroups()
{
    var rnd = new Random();
    var groupNumber = 0;
    var i = 0;
    while (i < BasketballCup.TeamsCount)
    {
        groupNumber = rnd.Next(0, GroupsCount);
        if (Groups[groupNumber].Count < TeamsInGroupCount)
        {
            Groups[groupNumber].Add(Teams[i]);
            i++;
        }
    }
}