233A. Perfect Permutation

A. Perfect Permutation

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

A permutation is a sequence of integersp₁, p₂, ..., p_n, consisting ofn distinct positive integers, each of them doesn't exceedn. Let's denote the i-th element of permutation p asp_i. We'll call numbern the size of permutation p₁, p₂, ..., p_n.

Nickolas adores permutations. He likes some permutations more than the others. He calls such permutations perfect. Aperfect permutation is such permutation p that for any i (1 ≤ i ≤ n) (n is the permutation size) the following equations holdp_pi = i andp_i ≠ i. Nickolas asks you to print any perfect permutation of sizen 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 printn distinct integers from 1 to n, p₁, p₂, ..., p_n — permutationp, that is perfect. Separate printed numbers by whitespaces.

Examples

Input

1

Output

-1

Input

2

Output

2 1 

Input

4

Output

2 1 4 3 

题意分析：求一个数列，每一项得值不超过n，而且 p_pi = i andp_i ≠ i . 第 i 项确定为某值 k 时即p_{i = k}则有，p_pi = p_{k = i}. 所以每两个项是对应确定得。当n为单数时，不能符合要求。由于p_i ≠ i ，只要把 第 i 和 i+1 项分别赋值为 i+1 ，i 就可以满足p_i ≠ i 的要求。

#include <stdio.h>int main()  {         int n;       scanf("%d",&n);       if(n%2!=0)              printf("-1");       else{              for(int i=1;i<=n;i=i+2){                     printf("%d %d ",i+1,i);              }       }              return 0;  }