#include <bits/stdc++.h>
using namespace std;
int main(void) {
  int n;
  cin >> n;
  if (n % 2 != 0) {
    cout << "-1";
  } else {
    int c[200];
    for (int i = 2; i <= n; i += 2) {
      c[i] = i - 1;
    }
    for (int i = 1; i <= n; i += 2) {
      c[i] = i + 1;
    }
    cout << c[1];
    for (int i = 2; i <= n; i++) {
      cout << " " << c[i];
    }
  }
  return 0;
}
