#include<iostream>
using namepsace std;
int main()
{
    int a;
    cin>>a;
    if(a>=0)
    {
        int num[a],sum=0;
        for(int i=0;i<a;i++)
        {
            cin>>num[i];
            if(num[i]>=0)
            {
            sum+=num[i];
            }
            else
            {
                cout<<"Invalid input";
            }
        }
        cout<<sum;
    }
    else
    {
        cout<<"Invalid input";
    }
}