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