#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int arr[101];
  for (int i = 1; i <= n; i++) arr[i] = i;
  for (int i = 1; i < n; i = i + 2) {
    swap(arr[i], arr[i + 1]);
  }
  if (n % 2 != 0)
    cout << "-1";
  else
    for (int i = 1; i <= n; i++) cout << arr[i] << " ";
}
