#include <bits/stdc++.h>
using namespace std;
void show(vector<long long> v) {
  for (auto it = v.begin(); it != v.end(); ++it) {
    cout << *it << " ";
  }
  cout << "\n";
}
void solve() {
  long long n;
  cin >> n;
  if (n % 2 == 1)
    cout << "-1";
  else {
    for (long long i = 0; i < n / 2; i++) {
      cout << 2 * i + 2 << " " << 2 * i + 1 << " ";
    }
  }
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}
