Description
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.

Examples
Input
1
Output
-1
Input
2
Output
2 1
Input
4
Output
2 1 4 3
C語言版本一

#include <stdio.h> #include <stdlib.h>/* run this program using the console pauser or add your own getch, system("pause") or input loop */int main(int argc, char *argv[]) {int n;scanf("%d",&n);int i;if(n%2!=0){printf("-1\n");}else{if(n>2){for(i=1;i<=n-2;i++){printf("%d ",i+1);printf("%d ",i);i++;}}printf("%d ",n);printf("%d\n",n-1);}return 0; }

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