#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a[100];
  cin >> n;
  for (int i = 0; i < n; i++) {
    a[i] = i + 1;
  }
  int j = 1;
  for (int i = 0; i < n; i = i + 2) {
    if (n % 2 != 0) {
      break;
    }
    if (j == n)
      break;
    else {
      swap(a[i], a[j]);
    }
    j += 2;
  }
  for (int i = 0; i < n; i++) {
    if (n % 2 != 0) {
      cout << -1;
      break;
    }
    cout << a[i] << " ";
  }
}
