Perfect Permutation

最新推荐文章于 2019-08-04 21:00:56 发布

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本文介绍了一个简单的算法，用于生成特定类型的排列——完美排列。对于给定的整数n，如果存在一个长度为n的排列，使得对每个1到n的整数i都满足ppi = i且pi ≠ i，则该排列被视为完美排列。文章提供了判断并输出完美排列的C++代码实现。

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) (nis 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 ndistinct integers from 1 to n, p1, p2, ..., pn — permutation p, that is perfect. Separate printed numbers by whitespaces.

Examples

Input

Output

-1

Input

Output

2 1

Input

Output

2 1 4 3

AC代码（水题）

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main()
{
    int n, a[120];
    int i;
    while(scanf("%d",&n)!=EOF)
    {
        if(n%2!=0)
            printf("-1\n");
        else
        {
            for(i = 1;i<=n;i++)
            {
                if(i%2==0)
                   printf("%d%c",i-1,i==n?'\n':' ');
                else
                    printf("%d ",i+1);
            }
        }
    }
    return 0;
}