#include <bits/stdc++.h>
using namespace std;
int main() {
  int n1;
  cin >> n1;
  int s[n1];
  int z = 0;
  for (int i = 1; i <= n1; i++) {
    s[z] = i;
    z++;
  }
  if (z % 2 == 0) {
    int i = 0;
    int j = 1;
    while (j <= z - 1) {
      int temp = s[i];
      s[i] = s[j];
      s[j] = temp;
      i += 2;
      j += 2;
    }
    for (int a = 0; a < z; a++) {
      cout << s[a] << " ";
    }
  } else {
    cout << -1;
  }
}
