#include <bits/stdc++.h>
int main() {
  int n;
  while (scanf("%d", &n) != EOF) {
    if (n % 2 == 1) {
      printf("-1\n");
      continue;
    }
    printf("2 1");
    for (int i = 3; i < n; i = i + 2) printf(" %d %d", i + 1, i);
    printf("\n");
  }
  return 0;
}
