CodeForces 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 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

[code]#include<iostream>
#include<algorithm>
using namespace std;

int main(){
int n,i,d;
while(cin>>n){
if(n%2){
cout<<"-1"<<endl;
}
else{
d=n-2;
for(i=0;i<n;i+=2){
if(i==d){
cout<<i+2<<" "<<i+1<<endl;
}
else{
cout<<i+2<<" "<<i+1;
cout<<" ";
}

}
}
}
return 0;
}

[/code]