#include <bits/stdc++.h>
using namespace std;
vector<int> v;
int main() {
  int n;
  scanf("%d", &n);
  if ((n % 2) != 0) {
    cout << -1;
    return 0;
  } else {
    for (int i = 1; i <= n; i++) {
      v.push_back(i);
    }
    for (int i = 0; i < n; i += 2) {
      swap(v[i], v[i + 1]);
    }
    for (int i = 0; i < n; i++) {
      cout << v[i] << " ";
    }
    cout << endl;
  }
}
