#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  while (cin >> n) {
    if (n & 1)
      puts("-1");
    else {
      for (int i = 1; i <= n; ++i) {
        cout << (i % 2 ? i + 1 : i - 1) << ((i == n) ? "\n" : " ");
      }
    }
  }
}
