#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, arr[105], i;
  cin >> n;
  if (n % 2 != 0)
    cout << -1 << endl;
  else {
    for (i = 1; i <= n; i++) {
      if (i % 2 == 0)
        cout << i - 1 << " ";
      else
        cout << i + 1 << " ";
    }
    cout << endl;
  }
  return 0;
}
