#include <bits/stdc++.h>
int main() {
  int a, b;
  scanf("%d", &a);
  if (a % 2 == 0) {
    for (b = 1; b <= a - 2; b += 2) printf("%d %d ", b + 1, b);
    printf("%d %d\n", b + 1, b);
  } else {
    printf("-1\n");
  }
  return 0;
}
