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