#include <bits/stdc++.h>
using namespace std;
void maloosh_lazma() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
}
int main() {
  maloosh_lazma();
  int n, temp;
  cin >> n;
  int *x = new int[n];
  if (n % 2 == 1) {
    cout << "-1";
    return 0;
  } else {
    for (int i = 0; i < n; i++) {
      x[i] = i + 1;
      if (i % 2 == 0) {
        x[i]++;
      } else {
        x[i]--;
      }
      cout << x[i] << " ";
    }
  }
}
