codeforces#P804E. The same permutation
The same permutation
Description
Seyyed and MoJaK are friends of Sajjad. Sajjad likes a permutation. Seyyed wants to change the permutation in a way that Sajjad won't like it. Seyyed thinks more swaps yield more probability to do that, so he makes MoJaK to perform a swap between every pair of positions (i, j), where i < j, exactly once. MoJaK doesn't like to upset Sajjad.
Given the permutation, determine whether it is possible to swap all pairs of positions so that the permutation stays the same. If it is possible find how to do that.
The first line contains single integer n (1 ≤ n ≤ 1000) — the size of the permutation.
As the permutation is not important, you can consider ai = i, where the permutation is a1, a2, ..., an.
If it is not possible to swap all pairs of positions so that the permutation stays the same, print "NO",
Otherwise print "YES", then print 
lines: the i-th of these lines should contain two integers a and b (a < b) — the positions where the i-th swap is performed.
Input
The first line contains single integer n (1 ≤ n ≤ 1000) — the size of the permutation.
As the permutation is not important, you can consider ai = i, where the permutation is a1, a2, ..., an.
Output
If it is not possible to swap all pairs of positions so that the permutation stays the same, print "NO",
Otherwise print "YES", then print lines: the i-th of these lines should contain two integers a and b (a < b) — the positions where the i-th swap is performed.
Samples
3
NO
1
YES