#include <bits/stdc++.h>
using namespace std;
long long Bin_expo(long long n, long long b) {
  long long res = 1;
  while (b > 0) {
    if (b & 1) {
      res = (res * n);
    }
    n = (n * n);
    b /= 2;
  }
  return res;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  if (n & 1)
    cout << -1 << "\n";
  else {
    for (long long i = 0; i < n; i++) {
      if (i % 2) {
        cout << i << " ";
      } else
        cout << i + 2 << " ";
    }
    cout << "\n";
  }
}
