#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  if (n == 1) {
    cout << "-1\n";
    return 0;
  }
  if (n & 1) {
    cout << "-1\n";
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    if (i & 1) {
      cout << (i + 1) << " ";
    } else {
      cout << (i - 1) << " ";
    }
  }
  cout << "\n";
  return 0;
}
