#include<stdio.h>
int main(void)
{
	int n,m,sum,c,i;
	while(~scanf("%d",&n))
	{
		sum = 0;
		c=0;
		for(i=0;i<n;++i)
		{
			scanf("%d",&m);
			if(m>0)
				sum+=m/2;
			else
				sum+=m;
			if(sum<0)
				c++;
			
		}
		printf("%d\n",c);
	}
}