my @ranges = (
    [ 0, 5 ], [ 1, 6 ], [ 2, 7 ], [ 3, 8 ], [ 4, 9 ], [ 5, 10 ],
    [ 5, 0 ], [ 6, 1 ], [ 7, 2 ], [ 8, 3 ], [ 9, 4 ], [ 10, 5 ],
);