input:

3
1
111
110110
1101010
1111
111111

output:

-1
12
2 3
5 6
1 2
2 4
1 2
2 4
2 3
3 4
4 5
5 6
6 7
7 8
6
3 4
3 4
4 5
4 5
4 5
5 6

result:

wrong answer (l,r) is invalid (test case 2)