#include <bits/stdc++.h>
using namespace std;
int n, ar[109];
int main() {
  cin >> n;
  if (n & 1)
    cout << -1 << endl;
  else {
    for (int i = 1; i <= n; i++)
      if (i & 1)
        cout << i + 1 << " ";
      else {
        cout << i - 1;
        if (i != n) cout << " ";
      }
    cout << endl;
  }
  return 0;
}
