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