#include <iostream>
using namespace std;
long long ile, a[100000], suma=0;
int main()
{
cin >> ile;
for (int i=1; i<=ile; i++)
{
cin >> a[i];
if (a[i]<0)
{
a[i]=0; a[1]=0; a[ile]=0;
suma+= a[i];
}
else if (a[i]>0)
{
a[1]=0; a[ile]=0;
suma+= a[i];
}
}
cout << suma << endl;
return 0;
}
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