#include<iostream>
using namespace std;
class factory{
    public:
    static int total;
    static void add(int items){
        if(items<0)
        cout<<"Invalid Production";
        exit(0);
    }
    total+=items;
};
int Factory::total=0;
int main(){
    int n,x;
    while(n--){
    cin>>n;
    Factory::add(x);
    }
    cout<<Factory::total;
    return 0;
}