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