Codeforces-233A Perfect Permutation

Perfect Permutation

Problem Description

A permutation is a sequence of integersp₁,p₂,...,p_n, consisting ofn distinct positive integers, each of them doesn't exceedn. Let's denote thei-th element of permutation p asp_i. We'll call numbern the size of permutationp₁,p₂,...,p_n.

Nickolas adores permutations. He likes some permutations more than the others. He calls such permutations perfect. Aperfect permutation is such permutationp 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 givenn.

 

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,...,p_n permutationp, that is perfect. Separate printed numbers by whitespaces.

 

Sample Input

1

2

 

Sample Output

-1

2 1 

 题目意思：

给你一个n，则会有排列p1,p2,p3,p4...pn，并且pi<=n,；

如果n的某个排列满足：p_pi=i andp_i≠i.（1<=i<=n），则此排列为完美排列。

输出这个排列。。

可以找出规律，当n%2== 1 时，必定找不出符合条件的完美排列。。

所以有：

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