How can I handle this variation?

Find Maximum sum in an array such that no 2 elements are adjacent. In this, 1 more condition was also there that first and last elements should also not be taken together.

If it would have been without the last condition, that is, then I developed the following code wherein I take two variables, incl and excl and find out the values. It is as follows:

#include <iostream>

using namespace std;

int main (void)
{
    int i,n;
    cin>>n;
    int arr[100];
    for ( i = 0; i < n; i++ )
        cin>>arr[i];
    int incl,excl,excls;
    incl = arr[0];
    for ( i = 1; i < n; i++ )
    {
        if (incl > excl)
            excls = incl;
        else
            excls = excl;
        incl = excl + arr[i];
        excl = excls;
    }
    if (incl > excl)
        cout<<incl;
    else
        cout<<excl;
    cout<<"\n";
    return 0;
}

How can I modify this for that special case? Thanks!