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