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