## Problem G: Fabled Rooks

We would like to place n rooks, 1 ≤ n ≤ 5000, on a n×n board subject to the following restrictions
• The i-th rook can only be placed within the rectangle given by its left-upper corner (xli, yli) and its right-lower corner (xri, yri), where 1 ≤ i ≤ n, 1 ≤ xli ≤ xri ≤ n, 1 ≤ yli ≤ yri ≤ n.
• No two rooks can attack each other, that is no two rooks can occupy the same column or the same row.

The first line of input contains one integer number, n, the side of the board. n lines follow giving the rectangles where the rooks can be placed as described above. The i-th line among them gives xli, yli, xri, and yri.

Your task is to find such a placing of rooks that the above conditions are satisfied and then output n lines each giving the position of a rook in order in which their rectangles appeared in the input. If there are multiple solutions, any one will do. Output IMPOSSIBLE if there is no such placing of the rooks.

```8
1 1 2 2
5 7 8 8
2 2 5 5
2 2 5 5
6 3 8 6
6 3 8 5
6 3 8 8
3 6 7 8
```

### Output for sample input

```1 1
5 8
2 4
4 2
7 3
8 5
6 6
3 7

```

K. Diks, adapted by P. Rudnicki
ACPC 2006