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