#include <bits/stdc++.h>
using namespace std;
void FST() {}
int32_t main() {
  FST();
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long int n;
  cin >> n;
  if (n % 2 != 0)
    cout << -1;
  else {
    long long int i = 2, j = 1;
    for (long long int k = 0; k < n / 2; k++) {
      cout << i << " " << j << " ";
      i += 2;
      j += 2;
    }
  }
  return 0;
}
