Please, try EDU on Codeforces! New educational section with videos, subtitles, texts, and problems.
×

Virtual contest is a way to take part in past contest, as close as possible to participation on time. It is supported only ICPC mode for virtual contests.
If you've seen these problems, a virtual contest is not for you - solve these problems in the archive.
If you just want to solve some problem from a contest, a virtual contest is not for you - solve this problem in the archive.
Never use someone else's code, read the tutorials or communicate with other person during a virtual contest.

No tag edit access

E. Restore the Tree

time limit per test

3 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputPetya had a tree consisting of *n* vertices numbered with integers from 1 to *n*. Accidentally he lost his tree.

Petya remembers information about *k* vertices: distances from each of them to each of the *n* tree vertices.

Your task is to restore any tree that satisfies the information that Petya remembers or report that such tree doesn't exist.

Input

The first line contains two integers *n* and *k* (2 ≤ *n* ≤ 30 000, 1 ≤ *k* ≤ *min*(200, *n*)) — the number of vertices in the tree and the number of vertices about which Petya remembers distance information.

The following *k* lines contain remembered information. The *i*-th line contains *n* integers *d* _{ i, 1}, *d* _{ i, 2}, ..., *d* _{ i, n} (0 ≤ *d* _{ i, j} ≤ *n* - 1), where *d* _{ i, j} — the distance to *j*-th vertex from the *i*-th vertex that Petya remembers.

Output

If there are no suitable trees, print -1.

In the other case, print *n* - 1 lines: each line should contain two vertices connected by edge in the required tree. You can print edges and vertices in an edge in any order. The tree vertices are enumerated from 1 to *n*.

If there are many solutions print any of them.

Examples

Input

5 2

0 1 2 3 2

2 1 0 1 2

Output

2 1

3 2

4 3

5 2

Input

3 1

1 2 1

Output

-1

Note

Picture for the first sample:

Codeforces (c) Copyright 2010-2020 Mike Mirzayanov

The only programming contests Web 2.0 platform

Server time: Jul/07/2020 06:46:20 (i2).

Desktop version, switch to mobile version.

Supported by

User lists

Name |
---|