#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> arr(101);
int main() {
  cin >> n;
  if (n % 2 != 0) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 1; i <= n - 1; i += 2) {
    arr[i + 1] = i;
    arr[i] = i + 1;
  }
  for (int i = 1; i <= n; i++) cout << arr[i] << " ";
  cout << endl;
}
