#include<iostream>
using namespace std;
class Machine{
    private:
    static int totalProduction;
    public:
    static void addProduction(int items){
        totalProduction += items;
    }
    static int getTotal(){
        return totalProduction;
    }
};
int Machinr::totalProduction = 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::addProduction(items);
    }
    cout<<Machine::getTotal()<<endl;
    return 0;
}