30分，后四个RE，那30怎么来的懂的都懂QAQ
MY code:```

#include<bits/stdc++.h>
using namespace std;
int main()
{
int s,a[1025],n,i,q=0;
cin>>n;
if(n%2!=0)
cout<<"-1";
else
{
    for(i=2;i<=n/2;i=i+2)
    {
       a[i]=i;
    }
    for(i=n/2;i>=2;i=i-2)
    cout<<a[i]<<" ";
}
return 0;
}