#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int y = 1;
  cin >> n;
  int arr[1000];
  if (n % 2 != 0) {
    cout << "-1" << endl;
  } else {
    for (int i = 0; i <= n; ++i) {
      arr[i] = y;
      y++;
    }
    for (int i = 0; i < n; ++i) {
      swap(arr[i], arr[i + 1]);
      i++;
    }
    for (int i = 0; i < n; ++i) {
      cout << arr[i] << endl;
    }
  }
  return 0;
}
