public static void Main()
var numbers = new [] { 5, 1, 2, 3, 4, 3, 5, 6 };
for (var turtleIndex = 0; turtleIndex < numbers.Length; turtleIndex++)
var turtle = numbers[turtleIndex];
var turtleRightIndex = turtle - 1;
var hare = numbers[turtleRightIndex];
if (turtleRightIndex != turtleIndex && turtle == hare)
Console.WriteLine(turtle);
numbers[turtleIndex] = hare;
numbers[turtleRightIndex] = turtle;