#include <bits/stdc++.h>
using namespace std;
int main() {
  int a[101];
  for (int i = 1; i < 101; i++) a[i] = i;
  for (int i = 1; i < 101; i += 2) swap(a[i], a[i + 1]);
  int n;
  cin >> n;
  if (n & 1)
    cout << -1 << "\n";
  else
    for (int i = 1; i <= n; i++) cout << a[i] << ' ';
}
