CodeForces

CodeForces - 233A

A permutation is a sequence of integers p1, p2, ..., pn, consisting of n distinct positive integers, each of them doesn't exceed n. Let's denote the i-th element of permutation p as pi. We'll call number n the size of permutation p1, p2, ..., pn.Nickolas adores permutations. He likes some permutations more than the others. He calls such permutations perfect. A perfect permutation is such permutation p that for any i (1 ≤ i ≤ n) (n is the permutation size) the following equations hold ppi = i and pi ≠ i. Nickolas asks you to print any perfect permutation of size n for the given n.

Input

A single line contains a single integer n (1 ≤ n ≤ 100) — the permutation size.

Output

If a perfect permutation of size n doesn't exist, print a single integer -1. Otherwise print n distinct integers from 1 to n, p1, p2, ..., pn — permutation p, that is perfect. Separate printed numbers by whitespaces.

Example
Input

1Output-1Input2Output2 1 Input4Output2 1 4 3 

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;int main()      {          int n;          scanf("%d",&n);             if(n%2)                  printf("-1\n");              else                  for(int i=1;i<=n;i++)                  if(i%2)                  printf("%d%c",i+1,i!=n?' ':'\n');                 else                  printf("%d%c",i-1,i!=n?' ':'\n');            return 0;      }