There are n computer classrooms at the Ural State University.
On Saturday, October 9, it was decided to hold n programming
contests in a row! Organizers have drawn a schedule—a table of
size n × n of zeroes and ones. The jth number
in the ith row is equal to one if the jth classroom is occupied
during the ith competition, in the other case it is equal to zero.
On Friday, a cleaning lady Zina reminded organizers that she needed to tidy up the
classrooms after the contests. She planned to tidy up the first computer
classroom immediately after the first contest, tidy up the second classroom
after the second contest, and so on. Of course, the contests can't be held
in the classroom neither while they are being tided up nor after that.
Chairman of the jury agreed with Zina. At one operation he can choose a pair of
distinct integers i and j
(1 ≤ i, j ≤ n), swap the ith and
jth row in the schedule, and then immediately swap the ith
and jth column. The chairman is able to perform at most two hundred
such operations until the evening. Will he be able to make the schedule
acceptable to Zina?
Input
The first line contains an integer n (2 ≤ n ≤ 100).
The following n lines contain n numbers each and define the
schedule of contests.
Output
If the chairman does not have enough time to fix the schedule, output “−1”.
Otherwise, output the required number of operations t in the first row,
and then output t lines with two numbers in each, specifying the values of
i and j which should be chosen by the chairman for the next operation.
If there are many ways to fix the schedule you should output any of them.
Samples
input  output 

3
0 0 0
1 1 0
1 1 0
 1
1 3

3
1 1 1
1 1 0
1 0 0
 1 
Problem Author: Alex Samsonov
Problem Source: XV Open USU Championship