Perfect Permutation

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 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.

Sample Input

Input

1

Output

-1

Input

2

Output

2 1 

Input

4

Output

2 1 4 3 

---

只有偶数有答案，两两翻转。

#include<cstdio>#include<iostream>using namespace std;int main(){    int n,i;    while(cin>>n){        if(n%2){            cout<<"-1"<<endl;        }        else{            for(i=1;i<=n;i+=2){                if(i==n-1){                    cout<<i+1<<" "<<i<<endl;                }                else{                    cout<<i+1<<" "<<i<<" ";                }            }        }    }    return 0;}