#include <bits/stdc++.h>
using namespace std;
int scan() {
  int t = 0, m = 1;
  char c;
  c = getchar();
  while ((c < '0' || c > '9') and c != '-') c = getchar();
  if (c == '-') {
    c = getchar();
    m = -1;
  }
  while (c >= '0' && c <= '9') {
    t = (t << 3) + (t << 1) + c - '0';
    c = getchar();
  }
  return (t * m);
}
int main() {
  int n;
  cin >> n;
  if (n & 1)
    printf("-1\n");
  else {
    for (int i = 1; i <= n; i += 2) printf("%d %d ", i + 1, i);
  }
  return (0);
}
