#include<iostream>
using namespace std;
class factory
{
    public:
    static int total;
    static bool addProduction(int items)
    {
        if (items<0)
        {
            cout<<"Invalid production";
            return false;
        }
        total +=items;
        return true;
    }
};
int factory::total=0;
int main()
{
    int n;
    cin>>n;
    for(int i=0; i<n;i++)
    {
        int items;
        cin>>items;
        if(!factory::addProduction(items))
        {
            return 0;
        }
    }
    cout<<Factory::total;
    return 0;
    
}