#include <bits/stdc++.h>
using namespace std;
long long pwr(long long base, long long p, long long mod = (1000000007LL)) {
  long long ans = 1;
  while (p) {
    if (p & 1) ans = (ans * base) % mod;
    base = (base * base) % mod;
    p /= 2;
  }
  return ans;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
int main() {
  ios_base::sync_with_stdio(0);
  int n;
  cin >> n;
  if (n % 2 != 0) {
    cout << "-1";
    return 0;
  }
  for (int i = 1; i <= n; i += 2) cout << i + 1 << " " << i << " ";
  return 0;
}
