#include <bits/stdc++.h>
using namespace std;
bool reverse(long long a, long long b) { return a > b; }
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, i;
  cin >> n;
  if (n % 2 != 0)
    cout << "-1"
         << "\n";
  else {
    for (long long i = 1; i <= n; i++) {
      if (i % 2 == 0)
        cout << i - 1 << " ";
      else
        cout << i + 1 << " ";
    }
  }
}
