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