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