#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-9;
const int INF = 1 << 28;
const long long INFL = 1LL << 62;
string res[] = {"NO", "YES"};
int main() {
  int n;
  cin >> n;
  if (n % 2 != 0) {
    cout << -1 << endl;
  } else {
    vector<int> v(n);
    for (int i = 0; i < n; ++i) v[i] = i + 1;
    for (int i = 0; i < n - 1; i += 2) swap(v[i], v[i + 1]);
    for (int i = 0; i < n; ++i) cout << v[i] << " ";
    cout << endl;
  }
}
