using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Competition
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.ReadLine();
            var a = Console.ReadLine().Split(' ').Select(x => Convert.ToInt32(x)).ToArray();
            int kop = 0;
            int result = 0;
            foreach (var i in a)
            {
                if (i == -1)
                {
                    if (kop == 0)
                    {
                        result++;
                    }
                    else
                    {
                        kop--;
                    }
                }
                else
                {
                    kop += i;
                }
            }
            Console.WriteLine(result);
        }
    }
}