#include <bits/stdc++.h>
using namespace std;
int main() {
  setlocale(LC_ALL, "TURKISH");
  long long int n;
  cin >> n;
  if (n % 2 == 0) {
    for (long long int i = 1; i <= n; i++) {
      (i % 2 == 1) ? cout << i + 1 << " " : cout << i - 1 << " ";
    }
  } else {
    cout << -1;
  }
  return 0;
}
