#include <bits/stdc++.h>
int main() {
  int n;
  while (scanf("%d", &n) == 1) {
    if (n % 2 == 1) {
      puts("-1");
      continue;
    }
    int a = 4, b = 3;
    printf("2 1");
    for (int i = 2; i <= n / 2; ++i) {
      printf(" %d %d", a, b);
      a += 2;
      b += 2;
    }
    printf("\n");
  }
}
