#include<stdio.h>

int main()
{
	int n,i,j,s[1000];
	while(scanf("%d",&n)!=EOF)
{
	int count=0,qiu=0;
	for(i=0;i<n;i++)
	{
		scanf("%d",&s[i]);

	}

	for(j=0;j<n;j++)
	{
		if(s[j]>0)
			count+=s[j]/2;
		if(s[j]<0)
			count+=s[j];
		if(count<0)
			qiu++;
	}

	printf("%d\n",qiu);
}

	return 0;
}