#include <bits/stdc++.h>
using namespace std;
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long fact(long long n) {
  if (n == 0 || n == 1) return 1;
  return n * fact(n - 1);
}
bool prime(long long n) {
  for (long long i = 2; i * i <= n; i++) {
    if (n % i == 0) return false;
  }
  return true;
}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long n;
  cin >> n;
  if (n & 1)
    cout << "-1";
  else {
    for (long long i = 1; i <= n; i += 2) {
      cout << i + 1 << " " << i << " ";
    }
  }
}
