#include <bits/stdc++.h>
using namespace std;
void swap(int &a, int &b) {
  a = a + b;
  b = a - b;
  a = a - b;
}
int main() {
  int t;
  cin >> t;
  if (t & 1) {
    cout << -1 << "\n";
  } else {
    int a[1000];
    for (int i = 0; i < t; i++) {
      a[i] = i + 1;
    }
    for (int i = 0; i < t - 1; i += 2) {
      swap(a[i], a[i + 1]);
    }
    for (int i = 0; i < t; i++) {
      cout << a[i] << " ";
    }
    cout << "\n";
  }
  return 0;
}
