233A-perfect-permutation.cpp

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