#include<stdio.h>
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		int i,a[n+1];
		for (i=1;i<=n;i++)
		{
			scanf("%d",&a[i]);
		}
		int lucky=0,qiu=0;
		for (i=1;i<=n;i++)
		{
			if (a[i]>0)
			lucky+=a[i]/2;
			else 
			lucky+=a[i];
			if (lucky<0)
			qiu+=1;
		}
		printf("%d\n",qiu);
	}
}