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