Жишээ тэстүүд

Оролт
1
1
Гаралт
-1
Оролт
2
1 2
Гаралт
-1
Оролт
4
1 2 3 4
Гаралт
1 2
Оролт
3
1 1 1
Гаралт
-1

Тэмдэглэл

In the first two samples the required pairs obviously don't exist.

In the third sample you can swap the first two elements. After that the array will look like this: 2 1 3 4$. This array is unsorted.