#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
int main(void){
	int xing,n,a,qiu;
	while(scanf("%d",&n)!=-1){
		qiu=0;
		xing=0;
		while(n--){
			scanf("%d",&a);
			if(a>0){
				xing=xing+a/2.0;
			}
			else{
				xing=xing+a;
			}
			if(xing<0){
				qiu++;
			}
		}
		printf("%d\n",qiu);
	}
}