#include<iostream>
using namespace std;
class Machine{
    static int totalProduction;
    public:
    static void add(int items)
    {totalProduction += items;}
    static int getTotal(){return totalProduction;}
};
int Machine :: toatlProduction = 0;
int main(){
    int n;
    if(!(cin>>n))return 0;
    for(int i=0;i<n;i++){
        int items;
        cin>>items;
        if(items<0){
            cout<<"Invalid Production"<<endl;
            return 0;
        }
        Machine::add(items);
    }
    cout<<Machine::getTotal()<<endl;
    return 0;
}