#include <bits/stdc++.h>
using namespace std;
int n, cnt;
pair<int, int> arr[210];
bool mark[210][4];
int mn, mx;
string str;
set<int> st;
int gcd(int a, int b) { return (b == 0 ? a : gcd(b, a % b)); }
int main() {
  cin >> n;
  if (n % 2 == 1) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 1; i <= n; i += 2) cout << i + 1 << ' ' << i << ' ';
  cout << endl;
  return 0;
}
