At the end of a trial an eccentric judge sentenced the accused individual to some number of years in prison. However, the judge pointed out that this individual should 'select' the number of years to serve by himself!

The judge placed 12 boxes on the circumference of a circle. Each box was numbered, theclockwise sequenceof numbers on the boxes was: 1, 3, 6, 11, 8, 4, 5, 9, 0, 2, 7 and 10. The sentenced man was told that there is a number of coins in each box; and theclockwise sequenceof numbers of coins was 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11. The sentenced man should select a box and the number of coins in the box would determine the length of his sentence.

However, before the man pointed to any box, he asked the judge whether he can get any additional information, namely, how many boxes have numbers which exactly match the number of coins they contain? The judge replied that such information could not be disclosed, as it would allow him to determine the empty box. The man thought a little and pointed to the empty box anyway!

How did he know? Which box did he point to?