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