#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  ios::sync_with_stdio(0);
  cin.tie(0), cout.tie(0);
  string s, c;
  long long y, x, n, mx = -1, sum = 0, arr[1000] = {}, zero = 0, l = 0, z = 0,
                     a, b, r = 0, cont = 0;
  map<int, int> mp;
  cin >> x;
  if (x % 2 != 0 || x == 0) {
    cout << "-1";
    return 0;
  }
  for (int k = 1; k <= x; k += 2) {
    cout << k + 1 << " " << k << " ";
  }
  return 0;
}
