Sudoku

Sudoku is a logic-based combinatorial number-placement puzzle. The goal is to fill a $9 \times 9$ grid with the digits 1 to 9 so that the following hold:

• Each row contains each digit from 1 to 9 exactly once.
• Each column contains each digit from 1 to 9 exactly once.
• Each of the nine $3 \times 3$ subgrids contains each digit from 1 to 9 exactly once.

Given a sudoku grid that is not yet finished, determine whether it contains a mistake. You do not need to check whether the grid is solvable.

The input describes the sudoku grid. The characters |, -, and + frame the $3 \times 3$ subgrids. The character . represents an empty cell. All other characters are digits from 1 to 9.

Print GRESKA if the board contains a mistake. Otherwise, print OK.

In the first example there is no mistake, so the output is OK. In the second example, the digit 5 appears twice in the ninth column, and the digit 5 also appears twice in the lower right $3 \times 3$ subgrid. In the third example, the digit 2 appears twice in the second column and the digit 6 appears twice in the seventh column, so there are two mistakes.