#include<stdio.h>

int main()
{
	int n, i, luck, qz;
	int a[1001];
	while (~scanf("%d", &n))
	{
		for (i = 0; i < n; i++)
		{
			scanf("%d", &a[i]);
		}
		luck = 0, qz = 0;
		for (i = 0; i < n; i++)
		{
			if (a[i] > 0)
				luck += a[i] / 2;
			else
				luck += a[i];
			if (luck < 0)
				qz++;
		}
		printf("%d\n", qz);
	}
	
	return 0;
}