#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;   }   