Sudoku!
Exactly what it says on the tin. Solve this sudoku, and you will procede. Fail, and you will go no further.
Pressing solve will leave in place the numbers you've entered so far, but leaving the page will erase them.
Here is a link to a full page image of the sudoku puzzle that you can print out and solve by hand before entering the numbers here.
If you have no idea how to solve a sudoku, don't forget you can work in groups!