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