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