perfect_permutation.cpp

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

int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
int n;
    cin>>n;
    if(n%2!=0) cout<<"-1"<<" ";
    else
{
      for(int i=1; i<=n;i++)
    {
        if(i%2==0) cout<<i-1<<" ";
        else cout<<i+1<<" ";
    }
}
    return 0;
}