#include<iostream>
using namespace std;
class m{
    private:
    int ip;
    static int tp;
    public:
    void rp(int items){
    if(items < 0)
        cout<<"Invalid Production"<< endl;
    }else{
        ip = items;
        tp += items;
    }}
    static int gtp(){
        return tp;
    }
    
};
int m :: tp = 0;
int main(){
    int n;
    cin >> n;
    m x;
    for(int i=0; i<n; i++){
        int items;
        cin >> items;
        x.rp(items);
    }
    cout << m::gtp()<<endl;
}