#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>

using namespace std;
int main()
{
	int n;
	while(cin>>n)
	{
		int a,sum=0,max=0;
		for(int i=1;i<=n;i++)
		{
			cin>>a;
			if(a>0)
				sum+=a/2;
			else sum+=a;
			if(sum<0)
				max+=1;
		}
		cout<<max<<endl;
	}
	return 0;
}