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