#include <iostream>
using namespace std;
class machine{
    public:
    static int total;
    static void add(int n)
    {
        total+=n;
        }
};
int machine::total-0;
int main()
{
    int n,val;
    if(!(cin>>n))
    return 0;
    while(n--){
        cin>>val;
        if(val<0){
            cout<<"Invalid production"<<endl;
            return 0;
        }
        machine::add(val);
    }
    cout<<machine::total<<endl;
    return 0;
}