#include <bits/stdc++.h>
using namespace std;
bool prime[101];
void SieveOfEratosthenes(int n) {
  memset(prime, true, sizeof(prime));
  for (int p = 2; p * p <= n; p++) {
    if (prime[p] == true) {
      for (int i = p * p; i <= n; i += p) prime[i] = false;
    }
  }
}
int main() {
  long long n, m;
  cin >> n;
  long long c[n + 1];
  if (n % 2 != 0) {
    cout << -1;
    return 0;
  }
  for (long long i = 1; i <= n; i++) {
    c[i] = i;
  }
  for (long long i = 1; i <= n; i += 2) {
    swap(c[i], c[i + 1]);
  }
  for (long long i = 1; i <= n; i++) {
    cout << c[i] << " ";
  }
}
