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