Codeforces_427A

// Codeforces 427A

#include <iostream>

using namespace std;

int main()
{
    int n, q, pol = 0, rez = 0;
    cin >> n;
    for( int i = 0; i < n; i++ )
    {
        cin >> q;
        if( q == -1 )
        {
            if( pol > 0 )
            {
                pol--;
            }
            else
            {
                rez++;
            }
        }
        else
        {
            pol += q;
        }
    }
    cout << rez;
    return 0;
}