#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  if (n % 2 != 0) {
    cout << -1 << endl;
    return 0;
  } else {
    for (int i = 0; i < n - 1; i = i + 2) {
      a[i] = i + 2;
    }
    for (int i = 1; i < n; i = i + 2) {
      a[i] = i;
    }
  }
  for (int i = 0; i < n; i++) {
    cout << a[i] << " ";
  }
  return 0;
}
