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