Normal sudoku rules apply. Additionally, every digit from1 to 9 appears exactly once on the two main diagonals. An area surrounded by a dashed line is called a cage. Digits may not repeat within a cage. A number in the upper left corner of a cage indicates the sum of the digits within the cage. The digits in the three red cages add up to 31, the ones in the two blue cages add up to 17 and the digits in the two green cages sum up to 18. For the repetition of digits, cages of the same colour count as separate, i.e. a digit may appear in two different cages of the same colour.