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