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