#include<stdio.h>
int main()
{
	int q,x;
	int n,m;
	while(scanf("%d",&n)!=EOF)
	{
		q=0;
		x=0;
		while(n--)
		{
			scanf("%d",&m);
			if(m>0)
				x+=m/2;
			else
				x+=m;
			if(x<0)
				q+=1;
		}
		printf("%d\n",q);
	}
	return 0;
}